Story related and can't be missed. Read on if you need help with the boss fight.
Baron Kane is the Chapter 3 boss. He has 3 attacks.
1. A slow melee attack.
2. A spell that will silence Fidget.
3. Spawn zombies.
You can get around all his attacks pretty easily just by doing aerial dust storm back and forth. That's pretty much the entire fight. Doing dust storm back and forth. Bring Deadly Delight (food item) if possible to cure silence. Projectiles will help make this fight go faster than just doing aerial dust storm.