Favorite hero from Dungeon.

I wouldn't say that only she (Ice Golem + Deadly Chill) can effectively eliminate the machinist; plus, a great additional hero can be obtained from her.

Heh... Kifira has Ice Golem, not Irbet. Deadly Chill is available to everyone; it's the Ice Golem that's a matter of luck.
Irbet's Dark Ritual can sometimes be very useful. And it's useful in itself.

Leto will only be effective with good luck. Otherwise, it's not that easy to get Darkness.