Gideon's Memorial is a rare Legendary Artifact card from Reality Fracture (FRA), collector number 198. Current market price: $0.33 (foil $0.48), TCGplayer market prices via Scryfall.
Creature tokens you control get +1/+0 and have vigilance. {T}: Add one mana of any color. Spend this mana only to cast a planeswalker spell. {1}{W}, Discard this card: It deals 4 damage to target attacking or blocking creature.