Midnight Gale is a cheap (3 power) little fighter with the Flying skill. It also has an Infiltrate ability: the first time it successfully attacks the enemy character (as opposed to an enemy unit) it gains the Lifesteal ability.
Which is ok: a flying unit with 4 attack strength and Lifesteal is worth having. But it's nothing special. And with only three health it can be taken out very easily by something as simple a Torch.
So in terms of power cost I think this is a reasonable card but I really don't know why it's a legendary. It's simply not that good.
This page written for Eternal version 1.19, Card Set 1 Last updated: 28-04-2017