Curate, connect, and discover
I think we should have seen Castiel pushing his vessel beyond human limits in a fight. Like, in a very gory way.
Castiel not bothering to heal his vessel until after the fight is over and everyone is dead. Just imagine a man-shaped thing with a hole in its head, its guts spilling out, its ribs showing—still standing, still clutching its blade, still coming after you.
He’d make a lovely horror creature.