Xolatoyac, the Smiling Flood is a mythic Legendary Creature — Salamander Serpent card from The Lost Caverns of Ixalan Commander (LCC), collector number 8. Current market price: $1.15 (foil $0.46), TCGplayer market prices via Scryfall.
Whenever Xolatoyac enters or attacks, put a flood counter on target land. That land is an Island in addition to its other types for as long as it has a flood counter on it. At the beginning of your end step, untap each permanent you control with a counter on it.