Dark Depths is a mythic Legendary Snow Land card from Ultimate Masters (UMA), collector number 241. Current market price: $3.31 (foil $8.77), TCGplayer market prices via Scryfall.
Dark Depths enters with ten ice counters on it. {3}: Remove an ice counter from Dark Depths. When Dark Depths has no ice counters on it, sacrifice it. If you do, create Marit Lage, a legendary 20/20 black Avatar creature token with flying and indestructible.