Teferi's Honor Guard is a uncommon Creature — Human Knight card from The List (PLST), collector number VIS-22. Current market price: $0.10, TCGplayer market prices via Scryfall.
Flanking (Whenever a creature without flanking blocks this creature, the blocking creature gets -1/-1 until end of turn.) {U}{U}: This creature phases out. (While it's phased out, it's treated as though it doesn't exist. It phases in before you untap during your next untap step.)