Thunderheads is a uncommon Instant card from GRN Guild Kit (GK1), collector number 27. Current market price: $0.05, TCGplayer market prices via Scryfall.
Replicate {2}{U} (When you cast this spell, copy it for each time you paid its replicate cost.) Create a 3/3 blue Weird creature token with defender and flying. Exile it at the beginning of the next end step.