|Level||Stats||Resistance (%)||Resistance (Linear)||Resistance (Other)|
Treasure will reflect your damage, the reflect may be any element. It can still be hit, but all the damage you do to him, you will also do to yourself and all other allies (excluding summons).
Each time you hit Treasure he will unbewitch 1 turn of your effects and remove 1 MP for 2 turns (dodgeable, can be stacked up to 5? times).
It may be useful to use up all your MP before you hit the chest, as you will likely lose them otherwise.
Treasure will be Unlockable the whole fight, and will run so you should trap him in a corner, or remove his MP if you can.
Treasure will trigger Helping Hand on turn 5 and every 2 turns after that, which will heal all attackers to full HP and kill all summons. The spell will only trigger if Treasure's HP is below 50% of eroded maximum.
As a Sacrier, you can try to stand in a corner square, block off its exit using a summon, and use Cooperation to swap places with Treasure, thereby trapping it in the square. You can then swap with your summon on your following turn, thereby trapping Treasure until the end of the fight.
The killing blow will be reflected at full power (not related to how much HP the Treasure has remaining) even after the Treasure is dead. If your HP is sufficiently low it is possible to fail the fight even as you manage to kill the monster.
Another way to easily kill the chest with minimal damage is to use the Spectral Scout and hit the chest through the Funerary Fire with Lazybeam and Haunting. This method will prevent all reflect damage and the only damage you will take will be from the poison or on the final hit.