It buffs them based on how many others you control and digs for more
It's hard to identify a single game where Faerie Mastermind played a pivotal role, but I ended up running him in nearly every one of my blue decks and I was never sad to draw him
Bonecrusher Giant has been an awesome substitution for one of these cards, and while Magma Jet has fallen from grace in much the same way as Flametongue Kavu, I see Twinshot Sniper as another great card to sub in here
All by himself, I might add
Bist du doch so weit gekommen
And if toughness is your goal, you need some of the highest-toughness cards out there like Unhallowed Phalanx, Charix, the Raging Isle, and Kharis & the Beholder (that last one not being legal for tournament play)