Sinking Feeling is a common Enchantment — Aura card from Shadowmoor (SHM), collector number 51. Current market price: $0.20 (foil $0.75), TCGplayer market prices via Scryfall.
Enchant creature Enchanted creature doesn't untap during its controller's untap step. Enchanted creature has "{1}, Put a -1/-1 counter on this creature: Untap this creature."