well my entire reply has been deleted let's add up:

Ok..im sure one of my players will surely like that PrC.
BUT
Crimson slash is like a very strong injury poison that gives no save.
even rogues need sacrfice 1d6 damage for con dmg.
terryfing exc is somehow like some ability the ghost faced killer (Comp Adventurer) have.
Sudden death, NO SAVE?! for the love of god save for the daze and for the kill directly, it too powerful.

The class have a nice backround and abilities, balancing his abilities and he is a very cool PrC.
Tip: Bonus feats maybe once with a different list of feats.