The whole series is here, and the first post explaining what is going on is here.
A note on links: Since the beginning, these posts have included links to OSE monster entries. Necrotic Gnome appears to be overhauling their site as part of a 2026 streamlining of the OSE collection (would have been nice if old links had redirected to the new ones, but I'm not going to look a gift SRD in the mouth). If I have time I may go back and fix all these links, but until I do, you can go here and see the OSE monster list.
A further note on the monster list: During the late summer of 2026, while I was editing the final posts in this series, OSE significantly revised its lists of monsters. Great for OSE's continued development as a system, but this exercise will stick to the old, simple, B/X list from our beginning post; I'm not going to go back and attempt to determine the placement of creatures such as the Tree-Beast of Tarktuktulak.
#113: Sprite. Quite similar to pixies, which we already covered as the “boring” ones. Sprites in OSE have a bit more to work with. Groups of five or more can curse someone, and they prank people instead of killing them, even after the offending party has attacked them. So the pixies are innocently trapped in the prison, while the sprites are intentionally making mischief. Tapping the Monster Overhaul again, we get a fly theme, and they’re drawing rude pictures. So they’re drawing graffiti all over the dungeon. They’re probably going to prank and ridicule PCs, but they could also be useful informants. Anyone willing to pull a suitably outrageous prank on a powerful monster could earn their friendship. Hm…
#17: Carcass Crawler. Why does OSE have an off-brand carrion crawler, but not equivalent rebranded monsters for the mindflayer and the beholder? Other retroclone and old-school/new-school systems are not shy about doing their own legally distinct versions of trademarked WotC monsters.
As an encounter, the OSE crawler is either trivial or a TPK. It doesn’t actually do any damage, and can only eat someone if “left in peace.” But it can attack eight times per round, and paralyzes people for 2d4 turns (on average, 50 minutes). PCs kiting it and peppering it with arrows can deal with it easily. A group surprised by it (or foolishly entering melee by choice) is asking for carcassification.
The Overhaul redirects to the monstrous vermin entry, which includes a carrion caterpillar that hits all the same beats. Lets treat the caterpillar aspect as literal and assume that this is the larval form of another monster. I already made a monstrous caterpillar, so I can just steal from myself. Adding the paralysis is nice. Imagine a caterpillar that paralyzes your entire party, eats your clothes off your body while you lie there helplessly, and then leaves you behind, naked but uninjured. TPK (total pants kill).
#2: Ape, White. The most confusing part of the OSE entry is the phrase “gorilla-like apes.” Gorillas… are apes? Anyway, they’re herbivorous, and enemies of our cavemen. Neanderthals hate this one weird ape.
Rolling on the Overhaul table, we get “retain hazy memories of their past lives as villagers, and sometimes watch and protect their descendants.” Is this an Uncle Boonmee situation? It certainly spices up an otherwise generic ape encounter. Perhaps the apes are the descendants of a village that was displaced for the construction of the prison. They would be a sympathetic faction, but highly mysterious, spiritual, and decidedly non-material. The neanderthals hate them due to a (probably misplaced) trust in the prison builders, who displaced the white apes when the complex was built.
#121: Treant. With the carcass crawler I mentioned the monsters that are legally distinct adaptations of WotC monsters; it is worth remembering that D&D from its beginning has likewise had monsters who were in turn borrowed from elsewhere.
The treant is a straightforward protector of nature, and the relatively recent redirection of the river into the dungeon provides a pretty easy basis for them to be agitated. These treants probably dwell among the dryads we previously learned about, but are further removed from the prison builders. WIth their very slow sense of the progression of human-scale events, they may only be dimly aware of the prison at all.
#73: Medium. If you’re wondering why OSE has no entries for “wizard” or “mage” but includes a “medium” entry, it is because that is the title for a novice magic-user. This was actually true of several previous entries, like the acolyte.
The Overhaul includes a lavish five pages for wizards. So we have a trio of junior wizards – Shorth, Zephiros, and Claar – wandering around in this dungeon. Why are they here? Their notable spells are (respectively) Silence, Vertigo, and Glittergust. Shorth has a headless, hairless lemur as a familiar. Zephiors has a wand of knock/lock (quite handy in a prison). Claar is a teaching assistant at Blackspine, their wizarding school, so they are probably boss the two undergrads around. Their area of study is hallucinations! For “why is this wizard in the dungeon” we get “retracing the steps of their mentor,” which fits. Their mentor is (or is rumored to be) a prisoner here.
#88: Orc. I have hundreds of words in my blog post drafts on orcs, racism, and associated RPG discourse. When I first read the Overhaul and looked up the orc entry, I learned that Skerples had covered the core of what I wanted to say better in a section on the orc page titled “The Problem of Evil,” essentially saying that orcs can be inherently evil, or they can be people like other creatures, but these two categories can’t be mixed. I believe that modern D&D keeps stepping on this rake because there is no coherent sense of this distinction.
For purposes of our current use-case, the orcs are harbingers of an invasion. Smoke on the horizon has signaled their approach. They can taste blood to learn secrets. Their prize tools are siege engines. They (apparently) seek to destroy the local religion.
So the orcs are here to undo the work of the celestial prison builders. Only a few patrols are present at the start of the scenario, but more appear, eventually displacing the external factions and using their siegeworks to dig into the prison. This provides a clock on a campaign set in the prison. They are not monsters that can be realistically beaten, but a force of nature that will eventually destroy the prison.
The Overhaul’s framing of orcs is rooted in rumors and suspicion, so there’s a strong chance that their motivation is somewhat different than what's described above. They may even prove to be a surprisingly pragmatic faction to deal with; more so than many of the prisoners and wardens, anyway.
#67: Living Statue. I think the classic animated statue has lost ground over D&D’s edition to the golems, with which it shares a lot in common. We can use the lawful crystal statue as a prison guardian. Their programmatic behavior means they serve faithfully, but they are inflexible and predictable, so the inmates are gradually isolating and destroying them.
#48: Golem. Convenient to do these two back to back. I was surprised to see how much OSE’s golem entry differs from the the standard lineup that is pretty familiar in modern D&D: flesh (Frankensteinned), clay (closest to the original idea of the golem), stone (much more like OSE’s living statue), and iron (magical robot). OSE instead includes amber (animal-shaped tracker), bone (four-armed, non-undead), bronze (giant-sized, heated by fire within) and wood (small and simple).
Amber makes the most sense for our prison, but we already have an escaped-prisoner-tracking monster, so we’ll pick the bronze golem because it is the weirdest.
#89: Owl Bear. The D&D classic. For all of its brand recognition, it is mechanically interchangeable with a non-owl bear, a problem that continues up through modern D&D, where none of its history in the game makes it an interesting monster. Others have blogged about what a missed opportunity owlbears are, and how they could be more interesting.
Our Overhaul-informed leaves “dry log-sized pellets full of bones” and its mood of madness is “manic digging.” We already have burrowing monsters well-represented, but we could place the owlbear in the treant/dryad forest on top of the prison, and their dig sites could be dangerous but useful points of access to the upper parts of the prison.
#112: Spider, Giant. Another classic. OSE has black widow (deadly poison), crab (camouflage), and tarantella (uncontrollable dancing). Choosing randomly, we get the last one. The Overhaul has armor as “if illuminated, as leather. In darkness, as plate+shield.” I love details like this that demonstrate how the Overhaul is willing to break from old-school orthodoxy when there’s a more interesting option. We’ll add extensive web spinning as a feature.
We’re in the home stretch. Just one more post after this, and we will be done with the entire OSE bestiary.
