Credits: Eyebags
You can summon mimics using the following commands.
- /summon rpg:mimic
- /summon rpg:mimic _large

Just like there are two types of chests - a smaller one and a big one, there are two mimics to match them. Small mimic deals only 4 damage per bite and has 15 hearts. The big one, however, not only has bigger health but also applies a blindness effect to the player.

Players are not the only prey in their taste - villagers will be suffering from those creatures quite a bit too. Chest Mimics can drop some decent loot, like emeralds or other ores.

Video:
How to install addons:
- Download addon straight from your device
- Find and open .mcpack or .mcworld files that you download earlier
- Click it to import into Minecraft Pocket Edition
- Open the game
- Create a new world or edit an existing world
- Scroll down to Add-ons section and select the ones you want to apply