Reef Worm is a uncommon Creature — Worm card from Modern Horizons 3 (MH3), collector number 271. Current market price: $0.24 (foil $0.31), TCGplayer market prices via Scryfall.
When this creature dies, create a 3/3 blue Fish creature token with "When this token dies, create a 6/6 blue Whale creature token with 'When this token dies, create a 9/9 blue Kraken creature token.'"