Gideon of the Trials is a mythic Legendary Planeswalker — Gideon card from Amonkhet (AKH), collector number 14. Current market price: $1.53 (foil $5.10), TCGplayer market prices via Scryfall.
+1: Until your next turn, prevent all damage target permanent would deal. 0: Until end of turn, Gideon becomes a 4/4 Human Soldier creature with indestructible that's still a planeswalker. Prevent all damage that would be dealt to him this turn. 0: You get an emblem with "As long as you control a Gideon planeswalker, you can't lose the game and your opponents can't win the game."