Stormsplitter is a mythic Creature — Otter Wizard card from Bloomburrow Promos (PBLB), collector number 154p. Current market price: $3.61 (foil $5.46), TCGplayer market prices via Scryfall.
Haste Whenever you cast an instant or sorcery spell, create a token that's a copy of this creature. Exile that token at the beginning of the next end step.