Why does Ghastly Wail ignore immunities?

[Fluffal Kyurem]

Just serve up some Evil Smiles and you'll be cheesing out stronger enemies in no time.

[mimizukari]

all you need to cheese out strong enemies is Megidolaon, almighty goes through all resists. (but then you get no One More!)

[Fluffal Kyurem]

Originally posted by Kurumi Tokisaki:

all you need to cheese out strong enemies is Megidolaon, almighty goes through all resists. (but then you get no One More!)

But Ghastly Wail always instant kills.