Hydroid Krasis is a mythic Creature — Jellyfish Hydra Beast card from Ravnica Allegiance Promos (PRNA), collector number 183p. Current market price: $0.88 (foil $2.86), TCGplayer market prices via Scryfall.
When you cast this spell, you gain half X life and draw half X cards. Round down each time. Flying, trample This creature enters with X +1/+1 counters on it.