Bob

Bob Cassador Kai Dabastabar is an optional boss in Death Company. After defeating, he joins the party and teaches Casper Mad Rage.

Involvement in Plot
Bob can only be found in chapter 1, sitting on a weird carpet in Great Pyramid City. If you talk to him, he will unlock Casper's Mad Rage spell, which is quite useful, but then you have to defeat him. After that, he joins your party.

He is technically optional, but taking him unlocks an optional dungeon which contains many tresures that unlocks a few of your character's skills.

If you defeat him in chapter 1, he also joins your party in chapter 2 with a new skill and extra stats.

Battle
Because Bob is -elemental, Casper is weak against him (always does 1 damage). He can kill Casper quite easily, so make sure Marius heals Casper if needed. Since he's weak against, use Marius' Zeus' Thunder spell. That gets him down to 40% HP in one blow, but he full heals himself.

The simplest way to defeat him is to keep draining his soul and using Zeus' Thunder. This will kill him very quickly.