<3sRichardSimmons
Arcane
The Traitor Lord used to be more of a pushover but got beefed up in some update and now deals two points of damage per hit. Sharp Shadow is the easiest way to beat him.
IIRC he is an optional boss. All the main bosses are very easy. Optional content is more difficult.
He's technically optional, but only if you want the worst ending, otherwise you need to kill him to get the Kingsoul.
Elwro Having Cloth present and getting the Pure Nail make Traitor Lord a lot easier. I personally don't find Sharp Shadow to be that useful for the fight, but if you have the notches to spare might as well go ahead. But for what it's worth I think Colosseum is way easier than Traitor Lord.