Robber Trapper (Bose)
A monster lurking in treasure chests. It explodes when defeated, so kill it from afar.
x4 x2 x3 x3 x3 x3 x3
Don't bother with physical attacks and hit the Robber Trapper with any of your ranged arts. Not only does it have a high defense, but the damage it does when defeated might wipe out your entire party.