Dark Depths is a mythic Legendary Snow Land card from Secret Lair Drop (SLD), collector number 1680. Current market price: $12.34 (foil $13.73), 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.