Quote Originally Posted by Resileaf View Post
According to Cu Chulainn's lore in the Fateverse, his Noble Phantasm is pretty much guaranteed to kill whoever he attacks unless there's a higher power or plot armor preventing it. In-game, his skillset makes him powerful enough that he is one of the absolute best servants in the entire game. His rarity does not match his power level, both in lore and mechanically.
That's true, it's not an absolute measure, given the disparity in power even among the same rarity, and outliers like our bussy Cu.