You'd better hope you grabbed some effective removal or you'll be taking a loss real quickly
He's payoff and engine both for the popular spell-slinging archetype and even has a few easy infinite combos - and he's not the only Final Fantasy card that can be broken this way
Lifegain also overlaps heavily with two other archetypes worth raiding for pieces: vampire aristocrats (Vito, Epicure, Licia all live here) and go-wide tokens (every token that enters is a Soul Warden trigger)
7 Aladdin, Heroic Outlaw The second of the Emerald/Ruby decks face cards, Aladdin is a great way to pull an opponent storming ahead back down to earth
Toby, Beastie Befriender does a lot of stuff right, and it works well with populate, blink, tokens, and more
Although limited to certain strategies, Crusade can significantly bolster your minions chances for success