D and December 2017: Week 4 - Day 2(Belated)

2- Mimic/Trap

“Today I prepared Explosive Runes . . .”

Many years of playing & Gming, you create, steal & encounter numerous traps, some even become punch lines (as above).
That exact joke ran for years in a game, and never happened.
So, I decided it must be executed.
An Admantine Spellbook, with false "pages", that contained an actual spellbook (like a book safe), but the first "page" had Explosive Runes cast on it, so it could blow up in the holder's face and not damage the actual spellbook locked inside.

Similarly, having a delayed fireball as part of a treasure chest or secure room is a ton of fun as the group thinks they got past the trap, only to realize it had been sprung.

Another favorite is the "invisible wall".
It bisects a room or hallway, it's dimensions are 2 feet off the ground to 8 feet off the ground.
The trick is to describe it so that the party has to think about it/try different ways to "see"/work with the wall, to get over or under it.
This can be expanded as desired for more insidious uses (making the wall "deeper" so they have to crawl under for a distance, or across the top of it, place items or creatures in it/around it, etc)