This is an expansion off of MasInYoFace's Mimics in Vanilla Minecraft. The youtube video is his creation. My version is simpler and requires no slab floors. When you open the trapped chest, a command block destroys it, and spawns in a Mimic. The code for /summon Mimic is: "/summon Zombie 866 57 0 {IsBaby:1,Equipment:[{},{},{},{},{id:chest,Count:1}],ActiveEffects:[{Id:14,Amplifier:1,Duration:19999980,ShowParticles:0b}]}". The end command block just resets the repeater to unpowered. My new Mimics are just invisible zombies, with chests on their heads. Just to be clear, the video was made by MasInYoFace and I'm just making a new and improved version.