Mimics are a type of monster encountered in Fate.
Mimics are creatures whose bodies greatly resemble treasure chests. They're capable of standing completely still and pretending to be an ordinary Large Chest. When encountered, Mimics remain motionless and only become active when you try to open them, at which point they reveal their bat-like wings, tiny eyes, and enormous fangs, and begin pursuing you to engage in melee combat by biting you.
Mimics are pretty resilient creatures in general, but their most alarming attribute is their 100% resistance to Fire, Ice, and Electric damage; this makes them completely immune to most magic attacks.