Visions of Mana

The Black Rabite is an optional post-game boss that can be found in the Distorted Sanctum. You probably came across a tower during the story that you couldn't enter - this is where the Rabite is located (in the Mt. Gala section). The easiest way to go about this fight is simply to put it on Beginner difficulty and then you'll get unlimited resurrections in the event that all your characters die. The boss is Level 80 and hits extremely hard, and at 25% health splits into three different versions of itself who all have a full health bar and have to be defeated before resuming the fight. It's really kind of ridiculous, so I'd highly suggest going for the cheese on Beginner difficulty. You can largely use the same strategy as The Spawn of Calamity (90G) for your party setup and attacks either way you go about it.