This encounter was designed as a setpiece for a funhouse dungeon, but the conceit behind it could work in a number of different contexts - it could be the subject of a quest, or a status inflicted by an eccentric wizard or fey spirit, for instance. Feel free to adapt it as you wish.
While exploring the dungeon, the party comes upon an area that abides by strange rules. Depending on your goals (or how long you think your players are willing to put up with it), this area could be as small as a single room or as big as an entire floor. Either way, it should be obvious that something isn't right when the PCs enter this area. The ceiling is replaced by a stark white sky, and the surroundings are dominated by bizarre features - tall tree trunks that end in pink puffs, staircases leading to nowhere, and narrow pathways high off the ground supported by elaborate arches.
There can be any number of puzzles, traps, and encounters within this area - however, one rule that abides through all of them is that all creatures within this region must communicate in rhyme. Any in-character dialogue spoken aloud must be communicated in the form of rhyming couplets. All creatures entering this region of the dungeon will know this rule upon arriving, but will not know what happens if they fail to speak in rhyme. Optionally, if you want an extra challenge (and you really want your players to hate you), you can mandate that all dialogue out of character must rhyme as well.
It is acceptable to make up words in order to rhyme statements with them (in fact, this is entirely in keeping with the atmosphere), but these words must be communicated in a way that makes them make sense in context, such as by making up a creature that the statement refers to. The words cannot merely be non-sequiturs. For example, "we must discover an exit to this dungeon, before we get eaten by a Glubbulous Fludgeon" is acceptable, but "we must discover an exit to this dungeon, scrumbgeon" is not.
If any creature does not complete a rhyme while under the effects of the curse, they are immediately stricken by a powerful electric shock. The first time a given creature fails to rhyme, the shock causes them 1d4 lightning damage. For every subsequent failure to rhyme, the die of damage goes up by one size - ie. the second failure causes 1d6 damage, the third 1d8, the fourth 1d10, the fifth 1d12, and any subsequent failures 1d20. Players will hopefully learn to be careful with what they say after a few misses.
Players may rhyme their statements with statements made by other players or the DM. If a player fails to make a rhyme, another player can make a save by interjecting with a rhyme for the last thing they said. For example, if Alice ends a statement with "we should all make camp under this arch," Bob can chime in with "That's a great idea, I sure am parched!" before the DM rolls damage. If this happens, neither player takes damage.
This effect ends whenever a creature leaves the area carrying the effect.

Nice! I was thinking of a riddle to communicate to the players how the rule works. This is what I came up with:
ReplyDelete"When a verse comes to a close,
another must follow wherever it goes"
It could be written above the door leading to the area, or maybe a magical creature or thing tells it to the party, like a pixie or a talking doorknob.