I've been thinking up lots of 'special' encounters lately. They're not all tricks, but quite a few are.
Regarding 'specials' Mentzer's Basic Set gives a good set of ideas to go by:
specialThe other day, thinking of the kinds of specials I'd like to include in the megadungeon. I wrote down my own list of types, which covers a bit of the ground above, but has a few other ideas as well.
A “special” is anything you place which is not normal, but is not a trap, monster, or treasure. Some typical specials are:
Alarm: Summons special monster, opens dungeon doors, or has no effect at all.
Illusion: A dungeon feature (stairs, room, door, monster, treasure, etc.) is not really there, but is merely a phantasm.
Map Change: A shifting wall moves after the party passes, cutting off their exit. They must find another way out of the dungeon. The wall shifts back after a time (1 turn, 1 hour, 1 day).
Movement: The room (or stairs, or door, or item) moves (turns, drops, closes, rises, etc.) unexpectedly. It might be stopped if a roll for surprise (often with - 1, - 2, or - 3 penalty) shows that the party reacts quickly enough to prevent it.
Pool: Magical water has a strange effect if touched (or drunk, or sprinkled on someone or something), such as healing, inflicting damage, changing an Ability Score, changing Alignment, making something magical for a time, invisible for a time, etc.
Sounds: The room (or item, or treasure) makes strange noises: moaning, screaming, talking, etc.
Statue: A large statue of a person, monster, or gadget (nearly anything you can imagine) is found. It may be valuable, magical, too heavy to move, alive, lonesome and willing to talk (maybe a liar), covering a trap door down, a treasure, etc.
Transportation: This could be a trap door leading up or down, secret stairs, elevator, magical portal to elsewhere (another room, another level, another dungeon), etc.
Trick Monster: This applies to any variation of a listed monster, such as: a skeleton who shoots its fingertips like a Magic Missile, a two-headed giant ogre, a “goop” dragon that spits green slime or grey ooze, a wild bore (a shaggy man who tells long,
dreary stories), a quarterling (half-sized halfling), a Mouth Harpy (who can’t sing but plays the harmonica), an Ogre Jelly (looks like an ogre, but . . .) Rock and Roll Baboon, and so forth.
Weird Things: You may let your imagination run, placing such things as: weapons which fly - attacking by themselves, talking skulls, a magic item or treasure firmly stuck to the floor (or wall, or ceiling), a magical area (zero gravity, reversed gravity, growth to double size, shrink to 1” tall; effect lasts until leaving the area), a huge creature recently slain (too big to fit through the corridors - “But how did it get here?”), and so forth.
Landmarks: large statuary, frescoes, altars, odd colors, etc.
"Key" Items: things that stand out and have some use elsewhere in the dungeon
Oddities: lingering spell effects, magic mouth, pools/fountains, weird zones, etc.
Puzzles: block passage until riddle, logic puzzle, etc. solved
Quest Giver: otherwise friendly creature will only help if PCs help it first
Transport: mundane or magical access to area normally not connected
Maps: maps, clues, hints about the dungeon, windows/scry points