Mimic mobs added to dungeons

I personally believe dungeons need a new challenge. While they have their charm,they are kinda disarmed easily with a torch,and then easily looted. A mimic would be interesting. A mob that would have a 50% chance of spawning,replacing one of the chests. It'd attack when you try to open it,and could potentially drop either chest loot,or unique loot including a new armor trim.