Mimic

I one of the fun (it was fun to me anyway) things for new players to fantasy role-playing games is after multiple encounters of either conventional foes (cultists, evil soldiers, bandits, etc) or classic Tolkeinesque fantasy creatures like orcs and goblins the first time they encounter something truly bizarre.  The early history of D&D is littered with unique and exciting creatures that could spring surprises on unsuspecting players.

No matter how sincere your players are in attempts to separate player knowledge from character knowledge sometimes the mechanics of the game can give away what's going on.  That's one of the things I really like about a well used Mimic.  A group can complete an entire combat encounter, drop out of initiative and start searching and healing and then when they open a treasure chest BOOM! Mimic!

The Mimic is a shape-changer that can disguise itself as a simple inanimate object like a door or treasure chest and then when an unknowing character touches the item strike with its sticky tendrils in an attempt to ensnare and eat the character. 

I'm not sure if/when this particular Mimic will try to get one of my PCs but I'm fairly certain when it happens I'll hear an expletive yelled out at the first sign of attack.

-Jay