Mimics are monsters that appear in every area of Vagante. They drop a item and some gold after being defeated and can be differentiated from normal chests by looking at the lock at the sprite. Compared to the normal chest, it has a slightly redder tint.
They will stand still until hurt or until a player comes close enough.
To notice the Mimic, there is one precaution you should take: look at the lock of the chest. When the Mimic is disguised it looks like a common chest, but it has a slightly red tint. Though it should be noted that Mimics have fairly low HP, so getting caught by them isn't a big issue