Pluto is a non-essential boss fight in Phantasie 2 (similar to Zeus in Phantasie 1). He has 500+ HPs, and gets 14 swings on his attack, in addition to party wiping spells.
Here's a clip of me beating him, and his death speech. Interestingly, even after you beat him - If you come into the Palace in one of the wrong entrances and hit the teleporters, he will attack you again.