While Animate Library turns your library into an artifact creature that slowly loses power over the course of the game, animating it on turn six is very likely still giving you a 20+ power creature
It reads super useful in many decks
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If you can reliably give haste to other creatures, this Tyranid can continue to provide value over the course of the game
Of course, it has to die to do that, which means your opponents have to choose if its worth sacrificing their creatures, being slowly pinged to death, or just biting the bullet and hoping theyre not your target
While I look at Omen and see a clunky Limited mechanic, other players see the potential for shenanigans