Stolen Board Game Mechanic: Divide-and-Choose Spells

Various types of boardgames and card games include “I cut, you choose” mechanics. One player divides a quantity of tokens, or cards, or some other discrete game element into two piles, then a different player gets to pick among those piles, with the first player receiving the remaining selection. Like unchosen picks accruing value, divide-and-choose is interesting because it is self-balancing. The divider is incentivized to make as even a split as possible, unless they have access to information the chooser does not, or believe that the chooser is otherwise unlikely to pick correctly.

How could we apply this to D&D-style games? Consider divide-and-choose as a magic system.

Assume each spell has three major effects. The caster separates them into one pile of two and a remaining pile of one. The target of the spell can choose either pile.

For example, imagine that Fireball had the following effects: Area Effect; Fire Damage; Burning Condition.

The caster divides; they offer the target either Damage OR Area Effect + Burning Condition. The target is low on HP, so they take the Burning Condition and Area Effect, which spreads the Burning Condition to several of their allies. 

Video games provide plenty of ideas for effects. Area and range, damage increases, damage over time, all kinds of “debuffs,” poison or disease, fear and charm, and so forth. 

Some care has to be taken to avoid making one choice much weaker or much stronger than the others, such that the divide-and-choose would become trivially obvious. But this approach also makes it possible to add niche effects that wouldn't otherwise be "worth" including.

Consider a spell that forms a cloud with the effects Poison, Obscuration, and Coughing. The Poison and Obscuration effects are probably more broadly useful, and would typically be split, so that at least one would apply. But if the target is a spellcaster, and Coughing could prevent them from intoning arcane words, it might be viable to divide such that Coughing is alone and Poison and Obscuration are together, forcing the target to accept both Poison and Obscuration if they want to avoid Coughing and be prevented from casting spells.

A spell is not necessarily limited to three choices. A higher-level spell could involve four, five, or more choices. But we should be careful about how many we offer; too many choices and the divider will take too long picking their piles, dragging the game to a halt.