Mana Leech is a uncommon Creature — Leech card from Urza's Saga (USG), collector number 141. Current market price: $0.26, TCGplayer market prices via Scryfall.
You may choose not to untap this creature during your untap step. {T}: Tap target land. It doesn't untap during its controller's untap step for as long as this creature remains tapped.