Once you have a sufficiently large enough creature, you just need a way to send it in without being blocked, like with a Rogue's Passage or any other card that can make it unblockable
Cards like Squee, Dubious Monarch in Standard can provide the celebration trigger each turn, and Voldaren Epicure and Bloodtithe Harvester can do it too
The second is that this only works on the first one cast, so they can cast Brainstorm to dig for something and then cast what they drew
With enough energy you could cast a number of 3 or less mana value creatures at instant speed
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