Nadaar, Selfless Paladin is a rare Legendary Creature — Dragon Knight card from Adventures in the Forgotten Realms (AFR), collector number 303. Current market price: $0.37 (foil $0.52), TCGplayer market prices via Scryfall.
Vigilance Whenever Nadaar enters or attacks, venture into the dungeon. (Enter the first room or advance to the next room.) Other creatures you control get +1/+1 as long as you've completed a dungeon.