He can put counters on creatures to trigger things like card draw, he can gain us life to help trigger cards like Aerith, and he can return Summon creatures from the graveyard to play
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Aether Revolt have different takes on typical mono-colored abilities, from Yahenni, Undying Partisan's indestructible sacrifice to Baral, Chief of Compliance combining the looting ability to draw and discard with the instant and sorcery loving of a control deck
Its looking specifically for the fourth mana, not every fourth mana
Having access to a card that can snipe a pesky enchantment, remove a creature (as long as you do the usually-trivial extra work of having a creature in play), or draw cards when neither of the other modes are relevant, means this spell is never going to rot in your hand