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Youll usually start with smaller spiders like Spiders-Man, Heroic Horde or Spider-Man, Brooklyn Visionary, which smooth out your setup by creating tokens or grabbing lands
Second place goes, somewhat surprisingly, to Elder Gargaroth
6 Avenger of Zendikar Big, silly creatures is green's entire thing, and one of the most popular cards for that is Avenger of Zendikar
And Heartfire Hero feels awesome in a variety of Standard aggro decks and with Colossus Hammer in other formats #10
Decks playing Gaea's Cradle are generally ones playing a ton of creatures, so it'll often generate enough mana to be able to cast your entire hand in just one turn