Necromantic Nightmares Part IV: Body Snatchers, Ghouljamming, Rotted Roots

Last time: A Third Corpse-Wagon Full of Necromantic Novelties: Railroads, Sharks, and Skeleton-Style Severance

Faction: Grave Robbers and Body Snatchers

Grave robbing and body snatching was a big thing in real history and real history didn’t even have necromancy. It should be orders of magnitude more popular in a magical fantasy world. There’s a lot to work with when looking at historical examples. Evocative slang (“resurrectionists”). Science and progress versus respect for religion and tradition. Educated elites versus the working class. Racism, if you’re playing in a game that wants to unpack heavy issues.

This subject is a good hook for all kinds of adventures, whether the PCs are working as grave robbers, being paid to stop them, or just tossed back and forth by the ceaseless whims of the funereal world. Consider just a few.

Random table: What are the competing interests creating conflict in and around the world of the grave robbers?

1. The thieves’ guild is hiring skilled rogues to crack mortsafes. Adventurers could work for them, or help the city watch catch these criminals.
2. The vengeful ghost of a prominent politician has sworn to destroy the town if body snatchers take the remains of any member of its family. A volunteer watch group is forming to guard against this eventuality. The complication is that no one is completely certain how many illegitimate children this politician had, and whether or not the ghost would count any such deceased persons as family. Better figure out who they are, and protect their graves to be sure.
3. The ghast who rules over the local cemetery is spreading rumors that great wealth is buried with various recently buried bodies, hoping to let the grave robbers do the hard work of digging, then grab the bodies (of both the dead and the foolish robbers) for itself.
4. A serial killer (perhaps a deceptive monster like a wererat, perhaps just a normal human) is using already-robbed graves as a place to hide his victims. The local resurrectionists are understandably concerned this will lead to a mob blaming them and seeking them out. One group of criminals is thus incentivized to stop the actions of another, even more grim criminal.
5. A marriage between two ghosts has created a complication in the execution of the will of the local potentate. With the help of a wisecracking skull that can cast Speak With Dead at will, adventurers must untangle the legal intricacies of these conflicting life-or-death bonds. 
6. Thieves are following body snatchers and plundering the graves of valuables after the bodies are removed (the body snatchers scrupulously do not take any valuable items from a grave, besides the body itself). The two factions are on the brink of a gang war, each accusing the other of immoral acts.

Location: The Hunger Ship

Before the spelljamming ark departed on its extraplanar journey, the shipwright-priests blessed it, entreating the stellar gods to ensure that no one would ever go hungry aboard the vessel. The blessing worked, but in a perverse way. When the ship strayed from its course and supplies ran out, the passengers found that they would not die of starvation. But their hunger was as strong as ever, and that hunger drove them to survive as ghouls. The ark continues to drift between the stars, full of ghouls fighting amongst themselves and waiting for unwary travelers to stumble on their ship.

Random table: Grim and ghoulish scenes from the cursed corridors of the Hunger Ship.

1. Ghoul-priests have welded iron cages over the mouths of fanatical flagellant ghouls. Prevented from feeding, these monsters are kept in a constant state of frenzy. (visual reference: the garrador from Resident Evil 4)
2. Gunnery ghouls lovingly tend to massive spiked hooks on long cables, ready to fire at passing ships to haul in a fresh meal. (visual reference: the reavers from Firefly)
3. Even as the hooks pull the targeted vessel toward the Hunger Ship, ghoul boarders will clamber up the chains, vying to be the first to taste new flesh. (visual reference: a hectic boarding scene from any pirate or naval movie) 
4. A dining hall filled with exotic "food" that is the refinement of hundreds of years of cannibalistic closed-loop "recycling." Ghoul aesthetes will (temporarily...) hold off on devouring anyone who can give them thoughtful critical input on their quality of the offerings; the ghouls are concerned they have been removed from the culinary world too long and may be out of step with current trends. (visual reference: some combination of the dining room from Texas Chainsaw Massacre, the forbidden food from Pan’s Labyrinth, and the bar in From Dusk Til Dawn)
5. The ghoul chirurgeon is relatively diplomatic by ghoul standards, offering to trade a prosthetic replacement for a PC’s tastiest-looking limb. The prosthetics are genuine, not a trick, and each one can do something that a normal limb cannot. (visual reference: Bruce Campbell in Escape from LA or Dr. Steinman in BioShock)
6. The ghoul ascetic abstains from eating living things, consuming only dead matter. They seek to lead the ghouls on the ships to a graveyard planet where they could feast on ethically sourced bones for eternity. A bit of a bore compared to the other ghouls, but basically a good fellow. (visual reference: peaceful Dreamland ghouls in Lovecraftian works)

Monster: Rootrot Treant 

Blood drips from a crude mouth of cracks and splinters. Corrupted by necromancy, this once-mighty  forest guardian now spreads decay. Deceptively slow-moving, when he scents living things he can flip over and walk on hundreds of surprisingly sturdy branches, like a wooden spider with far too many limbs, slamming his body down on his prey.

Necromancers in conflict with vampires for control of the local undead will sometimes use Rootrot Treants as guardians. Bristling with wooden “stakes,” few vampires will engage them in direct combat.

Modern statblock:

Rootrot Treant (huge undead plant) AC 16 (natural armor) HP138 Speed 30’ or 60’ (charge ending in a slam attack that leaves it prone)

RES Poison damage

IMM Poisoned, exhausted

Challenge 9 XP 5000

False Appearance (indistinguishable from dead tree when motionless, mainly works in fall/winter) 

Siege Monster (double damage to objects and structures)

Actions: Bite or Slam

Bite (melee): +10 / 3d6+6 piercing damage

Slam (melee) +10 / 4d10+6 bludgeoning damage and the Rootrot Treant falls prone and cannot move further that turn. Save STR DC 16 or restrained under the treant's bulk; ATH DC 16 to escape.

1/day when the Rootrot Treant rises from prone to standing, as a bonus action, it may spawn a field of rotted thorny vines harming all living things in the affected area (as Spirit Guardians, necrotic damage) 

Old-school statblock: 

Rootrot Treant AC 17 HD 8 HP 36 Att +7 bite (4d6) ML 12 MV normal or x2 normal, then if bite hits, treant falls on top of target and pins to the ground. Surprise on 1-3 at short range in environments with ample dead trees.

A Third Corpse-Wagon Full of Necromantic Novelties: Railroads, Sharks, and Skeleton-Style Severance

Last time: More Necromantic Novelties: Anathema, Bacteria, Dinobomb

Location: Necropolis Railway

Managing the dead is challenging enough when they stay dead. Managing them in a world of undeath is  more complicated by a whole order of magnitude.

The threat of the undead changes how societies handle corpses and remains. But for significantly large urban areas, the first order of business is to get the dead away from the living. Facilitating that process requires serious infrastructure, including a way to get the bodies from where they die to where they will be laid to rest. Depending on the setting, the railway can be a literal railroad, or a more low-tech equivalent (e.g., river barges pulled by beasts of burden on the shoreline).

What dangerous situations might adventurers find on the necropolis line or at its terminus?

1. Overrun cadaver carriage. Zombie unlife has spread amongst the corpses on one of the carriages, and now all the bodies within are trying to get out.
2. Plague rat outbreak. Rats attracted to the cemetery are carrying a virulent new disease. Rumors suggest it is causing the infected dead to walk from their graves, but this may be misinformation.
3. Charnel snuffer. A ghost snagged in the cremation chimney has inhaled enough necromantic energy to move about the crematoriums, blowing out the fires and slowing this crucial work.
4. Missing VIP. Some corpses are preserved, typically because the railway masters anticipate that they may someday be the subjects of magic like Speak With Dead or (in rare cases) Resurrection. One such cadaver is missing, and a frantic search is underway to locate it before it is accidentally destroyed.
5. Religious dispute. The burial grounds around the railway terminus were carefully laid out to keep the faithful of different sects from crossing paths, but a recent schism in the church has led to clashes and disputes over choice burial sites. An opportunistic wight hopes to amplify the violence and turn members of both sides to undeath amid the confusion. 
6. Expired Express. Unsubstantiated reports suggest that necromancers and grave robbers are disguising themselves as ordinary mourners to get through cemetery security. Board the train and investigate suspicious characters, without angering the legitimately grief-stricken travelers.

Monster: Mummy Shark

Undead sharks preserved in formaldehyde and covered in seaweed wrappings. The rot from their bite has a particularly fearsome reputation among sailors, as the pus that emerges from the wound allegedly warps and weakens the wooden parts of sailing ships. Creatures that die within a mummy shark’s stomach emerge as zombies at the next low tide. This blog cannot be held liable if your players begin to sing an obnoxious song after they hear you say the words “mummy shark.”

Modern statblock:

Mummy Shark (large undead beast) AC 13 (natural armor) HP 126 Speed 30’ (swim) or 10’ (a flopping and thrashing crawl on land) 

Challenge 6 XP 2300 

Actions: Bite + Dreadful Glare. 

Bite (melee): +9 / 3d10+6 damage, save CON DC 14 or contract mummy shark rot; can only recover HP while fully immersed in salt water, and ships on which the infected character travel suffer wear and tear at x3 normal rate.

Dreadful Glare: Save WIS DC 13 or frightened until end of mummy shark’s next turn; fail by 5 or more, paralyzed also.

Old-school statblock: 

Mummy Shark AC 13 HD 8 HP 36 Att +7 bite (2d10 + mummy shark rot (can only recover HP while fully immersed in salt water, and ships on which the infected character travel suffer wear and tear at x3 normal rate) ML 12 MV x2 normal swimming, half normal on land. Silent until it attacks, only harmed by magic or electricity, save WIS/PARA on first sight or paralyzed with fear until it attacks or moves out of sight.

Milieu: Skeletal Severance  

Necromancy is legal, but highly regulated. Anyone with healthy bones can sell the rights to the use of their skeleton for a set number of years after their death. 

The clergy condemn this practice, and many right-thinking people are at least… squeamish about such a transaction. But many who are struggling to make ends meet will decide that security in life is worth some indignity in death.

Adventure hook: When a painter with a record-setting skeletal service contract goes missing, the Necromantic Guild has a strong incentive to verify if they’re alive or dead. They will pay well for proof of death, and more for the recovery of the skeleton. But be wary; the church may interfere with your efforts, in the hopes that an unresolved claim will destabilize the skeleton trade. 

More Necromantic Nonsense: The Profane Dead, the Bacterial Ghost, and the Dinobomb

Last time: New Necromantic Monsters and Factions for Weirder Worldbuilding 

Milieu: The Profanity of the Undead

Inherent to the idea of undeath as traditionally understood in most folklore and derived fiction is a wrongness and a fundamental reversal of what that person (or their society) viewed as natural and holy in life. Undead should not be kinda vaguely, ambiently unholy – they should specifically reject, pollute, or invert the values of their pre-undeath society.

Random table: In what way are these undead profaning what was most holy to them in life?

1. Ghoul-minotaurs, mouths dripping with beef tallow, worship at a profane altar to Our Lady of the Abattoir. 
2. Deadwood-dryads and treant snags knock down healthy trees and suck the life out of green shoots.
3. Revived rust monsters galvanize metals instead of rusting them. Highly prized by dwarven metalworkers who are heretical enough to deal with necromancers. 
4. Skeleton-fish, repelled by bodies of water, hurl themselves against the doors and windows of the fishermen who caught them, silently begging for their killers to consume flesh they no longer possess.  
5. Shadow-beholders emit blinding shafts of darkness, haunting living eye tyrants and threatening to deprive them of their most precious sense.
6. Poltergeist-gargoyles enraged by the physicality the spirit can no longer embody, possess statues across the city, toppling them onto unsuspecting passerby.

Monster: Bacterial Ghosts 

Non-sapient animals generally do not project sufficient soul-stuff to create ghosts. But there are exceptions. For example, when particularly large numbers of microscopic organisms die suddenly, their collective extermination can produce a ghost large enough for people to perceive.

This ghost is amoeba-like, with its “mouth” forming on any of its appendages. It is sometimes mistaken for an ooze. It cannot communicate or even really think in a way that people understand, but can be frighteningly motivated, as undeath seems to give it a collective direction that its constituent organisms lacked in their single-celled lives.

Random table: What is the bacterial ghost doing right now?

1. Lurking in a pond, consuming algae until they can build a Swamp Thing-like body.
2. Plotting revenge, hoping to destroy the bleach factory responsible for their innumerable deaths.
3. Unliving symbiotically on a ghost sloth.
4. Possessing the micromancer who foolishly bestowed awareness on their colony.
5. Researching spells with names like “pierce membrane” and “corrupt mitochondria.”
6. Haunting the innards of the cow where they once dwelt while still alive.

Treasure: Necromantic Clothing and Equipment

Much of the ordinary clothing and gear that people use in their daily lives is obviously derived from living things. Usually such items are too far removed from life to be affected by necromancy. Usually.

A particularly diligent necromancer, taking the time to study the processes behind the creation of clothing, tools, and armor, can add a spark of unlife to such items.

Random table: What necromantic equipment is available for those with the stomach to use it?

1. Compass armor. Leather armor that retains the ability of the cattle to sense the planet’s magnetic field. The wearer instinctively aligns north-south when standing around idly for a turn or longer.
2. Silk-shroud robes. Fine silk robes with hidden pockets containing zombie silkworms. The silkworms will spin silk to repair any damage to the robes. With patience, the silkworms can be goaded to reshape the garment; for example, refashioning the robe into strong silk-rope to escape a tower.
3. Snakeskin belt. When unbuckled, the "clasp" is capable of biting to deliver deadly poison once per day. Wearing tough gloves or carrying antivenom is strongly recommended as it is easy to forget and receive a nasty bite while undressing at the end of a long adventuring day. Stylish.
4. Naptha bomb. Rock-oil from a natural seep. Looks a lot like alchemists' fire. When thrown like a grenade, the necromantic reagent reanimates whatever ancient animals decomposed into the oil. Unpredictable due to the unknown (and probably cross-contaminated) mix of biological matter that made up the oil, but the best-case scenario can produce a terrifying amalgamation of undead dinosaurs.

Next time: Yet More Necromantic Novelties: Necropolis, Shark, Severance

New Necromantic Monsters and Factions for Weirder Worldbuilding (Part 1 in an Undying Series)

Necromancy is part of the vanilla fantasy vernacular that informs many RPGs. You can't have your skeleton warriors and life-draining ghosts without some fiction explaining how these spirits are spooking the PCs. Some fiction really digs deep into what a setting defined by necromancy would look like. But many fantasy RPGs only scratch the surface. Let's grab our corpse-exhumation shovels and dig a little deeper.

Monster: The Griefer

Adventurers call it the griefer. It’s a dungeon ghost that can only possess a freshly-killed body. Immaterial and barely visible, the griefer will follow adventurers or dungeon factions around the dungeon, waiting for conflict to produce a suitable corpse to possess.

The longer the griefer lingers without finding a body, the more disruptive it becomes, leveraging what weak spiritual id it possess to generate alarming noises or frightening images, hoping to startle dungeon dwellers into deadly conflict.

Adventure hook: A griefer is piloting the body of an heir to a minor noble family. The sibling who is second in the line of succession badly wants the body returned, so they can prove that the heir is dead. The reward depends on retrieving the body in reasonably good condition. The griefer is very motivated to avoid capture... but its possession of the body is also staving off decomposition.

Milieu: Necroarchy

With age comes wisdom, and mere death does not change that equation. Indeed, serving as a living member of the city council is almost like an audition for service after death in a city where broad acceptance of necromancy makes this possible. The enormous round council table features seats for the living members, while the undead members’ skulls sit on ornate stands at their stations. 

Adventure hook: The council requires a quorum to make important decisions, but several of the council skulls have been stolen. The government is paralyzed by this bizarre and unprecedented theft. The living council members suspect each other of the crime. Or perhaps it is a rival city-state, seeking to undermine the dead city's power. What no one yet knows is that the thief is actually the former lover of one of the deceased members, who they seek to resurrect. They stole the other skulls only to draw suspicion away from them.

Faction: The Great Skeleton Army

Animated skeletons persist. Bleached and fleshless, they do not rot like zombies. Indifferent to the sun, they do not need to flee the light, as vampires and shadows do. Easy to create en masse, they can be raised even by a necromancer of relatively modest power. And they often persist long after their creator has died (and likely joined their ranks). The great skeleton army is one such example, inspired by great examples like this one.

No one remembers why the great skeleton army was created, or who they were originally intended to fight. It obeys no clear leader, although some skeletons mimic the roles of officers. 

Random table: Encounters amidst and near the Great Skeleton Army

1. Skull-scout. Catapulted ahead or dropped from the sky by skeletal birds, these disembodied skulls scout for activity and then report their findings after the army recovers them. Endowed with more intelligence than a typical skeleton, they are usually bored, and eager to chat with passersby.
2. Grave sapper. Skeletons that spent ages buried underneath the earth are particularly adept at digging. Travelers are in for a harrowing experience if they meet the sappers by stepping on a weak patch of ground falling into an active tomb-tunnel.  
3. Parallel travelers. Like small fish swimming alongside a shark because the big predator scares off smaller predators, some living people will travel in the wake of the skeleton army to protect themselves from living threats they feel are more dangerous.
4. Impressment gangboss. Gathering skeletons to swell the skelly ranks. They are supposed to find “naturally occurring” skeletons, but are not above sourcing them from the living when needed. "I swear these skeletons just fell off the back of a wagon, boss."
5. Skelevangalist. Seeks to free bony brethren from their meat-prisons. Will shush living creatures who attempt to speak to it, claiming it is listening to their “bones' voices.”
6. Camp followers. Not that kind! No boner jokes, please. Opportunistic humans will trade goods and services that skeleton soldiers can't manage themselves. 
7. Bone collector. Skeletal ragman who collects stray bones from the battlefields, offering its wares to skeletons that have lost pieces to time or turmoil. Humble and easy to miss, but secretly essential to the army’s (literal) cohesion.
8. Desiccated deserter. Fleeing the military life and eager to find a place among the fleshy world.

Next time: More Necromantic Nonsense: The Profane Dead, the Bacterial Ghost, and the Dinobomb

Class, Ancestry, Background — Choose Two, Drop the Other

Old-school games sometimes leverage the concept of race-as-class (also known as ancestry-as-class). An elf or a dwarf could be a character choice functionally equivalent to (and exclusive of) a class like cleric or magic-user.

Later editions of the game separate ancestry and class as distinct categories on separate axes; classes are defined by advancement, while ancestry is (usually) inherent and unchanging. But ancestry-as-class maintains its appeal in some OSR systems, as it simplifies character creation and makes it easier to “play up” what is distinctive about a non-human character. And other games have tried to find a happy medium between these approaches.

In that spirit, here’s an alternative way to split the difference between modern and old-school; pick two out of three among ancestry, class, and background, and just drop the third.

Ancestry and class, but no background. This is already implicitly pretty common in D&D. D&D 5E’s backgrounds are one of its better game design structures, but many players pay them little heed. They choose a background at character creation in order to pick up an extra proficiency or two, then forget about them soon after. Ancestry plus class, with no background, just formalizes this implicit choice. Whatever this PC did before the dungeon, it isn’t relevant to their new life of adventure.   

Both are dwarves, but their backgrounds are very different.

Ancestry and background, but no class. This is something like ancestry-as-class in old-school play, but with a background to give the character some more texture. Part of the appeal of ancestry-as-class is that it can take powerful abilities like darkvision, underwater breathing, or even flight and cordon them off from complementary class choices. Adding a background helps distinguish one dwarf from another, and give them a bit more personality. It’s easier to put some more mechanical weight on backgrounds too; one can extrapolate from the flavor text and ribbon abilities of the 5E backgrounds and imagine ways they would be more prominent in play without classes sucking up all their oxygen.

Class and background, but no ancestry. Obviously a character still has an ancestry. This choice simply means it isn’t mechanically relevant. In old-school D&D, this is something like what a human fighter or human wizard was; it was just taken for granted that humans were a “blank” in terms of ancestry, and possessed no special powers. But in modern play (or in games that mix play styles), that is worth reconsidering, because those games have tended to give humanity some mechanical heft (for example, a bonus feat in 5E). It takes a little extra work to reason out what an elf with no elf powers or a dwarf with no dwarf powers looks like, but I think it is possible. For example, a class-plus-background character may nominally be a dwarf, yet does not possess signature abilities like darkvision because they grew up on the surface, or in a subgroup of dwarves who otherwise just don’t naturally have darkvision.

Stolen Board Game Mechanic: Add Value to the Unpicked Choice

Spots is a push-your-luck dice game. Players take turns choosing action cards, which dictate how they roll dice that turn. After they take their turn, the action card they chose is exhausted for the round. When all but one action card has been chosen, all actions are refreshed and the process begins again. This is arguably a form of Dutch auction, although with accruing value instead of decreasing price.

Pretty straightforward, right? But there’s a small rule that is secretly important to the game. The final action card that was left unselected gains a token that allows for a one-time reroll of the dice. Whoever picks that action card next will get to keep any tokens that have accumulated on the card, and can spend those tokens later. So if the players favor certain cards over others (and most players will), the unpopular card(s) will gradually accrue additional value as more tokens accumulate.

This mechanic is great because it automatically "balances" the perceived power level of the options available to the players. It doesn't matter if that’s an actual play design imbalance, where some choices are better than others, or simply a preference among the players for a certain style of play. The imbalances between the choices are self-correcting over time, as some quantity of tokens will eventually bring a less-popular choice into competition with the more popular ones.

Consider applying this mechanic to discrete, mutually exclusive choices in an RPG. For example, consider downtime for a party of three PCs in a fantasy adventure game like D&D. Each time they return to town, each PC can choose one of the following (in addition to resting): level up, gather information, carouse, research, or shop. Only one player may choose each action, and each player only gets one choice.

Player A chooses leveling, player B chooses research, and player C chooses shopping. Gather information and carouse go unchosen, so they each get a token that allows for one in-session reroll of the dice. Whoever chooses these options in the future gets to keep any tokens associated with that choice. Even if carousing or gathering information goes several downtimes without being chosen, the accumulation of tokens will eventually compel someone to take them.

The 5E Megadungeon: Death, Magic, and Cats

Last week: Running a Megadungeon Campaign in D&D 5E

Last week we covered darkvision and laid out the factors that make 5E insufficiently lethal for typical megadungeon play. Now lets discuss some solutions.

Tailor monsters to make them punch harder, but also die faster. Tweaking monster stats is categorically easier than getting PCs to buy into house rules that lower their own character’s powers. In addressing a common complaint with 5E that combat tends to drag on, I’ve found it helps a lot to make monsters hit harder, but be less tough. With some relatively modest adjustments, it is easy to cut an eight-round slogfest down to a tight three-round nailbiter. Monsters leave a bigger dent in PC HP totals, but PCs also have the satisfaction of taking them down before the battle gets boring. 

Cap leveling up somewhere between levels 8 and 12. D&D 5E is tuned around the first two to three tiers of play. The second tier ends at level 8 and the third ends at level 12. The game is fun in the fourth and fifth tiers, but parts of it break down, and it is certainly not suited to megadungeon play. I ran several hundred sessions of 5E in a game that went from level 1 to beyond level 20, and while that campaign worked for location-based play at low levels (including quite a bit of time in the Caverns of Thracia), it was essentially obligated to transition to scene-based play at high levels.

A megadungeon campaign really needs to stay location-focused for its duration, and the easiest way to make that happen is to agree at the outset to cap the PCs’ level. You can choose where you want to cap the level based on which dungeon-bypassing powers you really want to limit. A series of posts from the early days of my blog attempts to catalog which 5E powers bypass dungeon obstacles at various tiers.

This will take some buy-in from the PCs, but make the case that it is required to run a cool megadungeon in 5E. Capping progress doesn’t even require an explicitly old-school perspective. The idea of “E6” D&D (which caps progression at level 6) came out of the crunchy 3.5 D&D world all on its own. And maxed out PCs can become powerful figures in the local area, engaging in domain-level play. If the players still aren’t convinced, a megadungeon campaign isn’t right for them anyway.

Limit where the PCs can rest. The average modern-style party will gravitate toward a simple gameplan: Fully unload on any antagonists they encounter, then pass out on the spot for eight hours. There's some variance based on group composition – a minority of classes in 2014 5E are optimized around short rests – but most 5E groups will have a majority of long-rest-oriented PCs like wizards and paladins who want a solid eight hours of sleep so they can once again go supernova on the next monster that looks at them funny.

You are going to have to disabuse them of the idea that it is OK to rest in the dungeon. For a lot of players, it’s going to take some convincing.

Out of character, tell the players that resting in the dungeon or the surrounding wilderness is highly dangerous. Have NPCs reiterate this in-character. Ultimately, the PCs will attempt it anyway, and you should adjudicate consequences firmly, demonstrating how hard it is to get a good long rest in the dungeon. Of course, if the players take clever precautions to secure a long rest in the dungeon, reward them.

Finally, if you don’t think this will be enough to motivate your players, discuss a house rule at session zero that long rests are simply impossible inside the dungeon. I’m trying to be conservative with the house rules here, but this one may be worth it. 

Leverage time and antagonists against long rests. If resting in the dungeon isn’t practical, most PCs versed in modern-style play will pragmatically come up with an obvious fallback solution; retreat quickly to safety after every combat encounter. This is not really a bad thing; smart OSR PCs will keep avenues of retreat open as well. 

But retreating after every fight will slow the game to a crawl. Fortunately, both old school games (strict time records and faction play) and story games (clocks and fronts) offer some tools to incentivize modern and trad players to play differently. 

Establish antagonist NPCs and factions early, and then telegraph to the players how they are advancing their agendas every time the PCs take a long rest. It may help to present the PCs with antagonists right from session zero. A good example is the conceit used in Electric Bastionland and other games; have the party start with a shared debt they have to pay off. It could be one of the powerful factions in the town, or in the dungeon itself. The important thing is that the debt-holding faction both has a reason to be  antagonistic toward the PCs and methods for creating time pressure. 

Magic is ridiculously abundant to the point where you solve most of the normal OSR challenges with cantrips that half the party have.

I agree with this in a general sense. Cantrips are one of my least favorite parts of 5E, and they trivialize many parts of the game that old-school play emphasizes. 

But the problem is really limited to a small subset of cantrips. The biggest use-case of cantrips is essentially providing a DPS floor for full spellcasters in combat. I don’t enjoy this design decision, but it fits with how modern play handles combat, and we don’t need to change combat much to empower the megadungeon experience.

The genuinely concerning cantrips are the ones that trivialize challenges outside of combat. If I was running a megadungeon in 5E, I would modify or rule out a few cantrips:

• Light and Dancing Lights would be the obvious ones to ban or nerf by “promoting” them to first level, per the discussion of visibility and darkvision in the previous post.
• Mage Hand should probably receive the same treatment, given how useful it is for manipulating traps and doors without risking oneself. It may still be worth the spell slot even if “nerfed” to first level. If a player is interested in the Arcane Trickster archtype (a rogue subclass), you may need to negotiate with them how to interpret this adjustment, as Mage Hand is baked into that archetype’s core powers.
• Guidance is not causing a problem for a megadungeon specifically, but it is bad game design, so I would probably ban it if I was cutting other spells anyway. 
• Minor Illusion is a consideration, although strictly adjudicating it can denude it of its worst applications. 

The rest of the cantrips in the 5E.2014 PHB are not really disruptive to megadungeon play. Non-cantrip spells are a resource expenditure question, and are essentially covered by the time pressure tools discussed above. Sure, having access to Fly or Dimension Door can subvert some dungeon challenges; but these are precious spell slots if we cap the PC's level somewhere between 8 and 12. 

So yeah, a 5E group is going to move through the megadungeon more quickly and suffer fewer casualties than an equivalent old-school group. But they're not going to trivialize a well-run megadungeon. 

Cat People???