Wall of Tombstones is a uncommon Creature — Wall card from Legends (LEG), collector number 129. Current market price: $5.27, TCGplayer market prices via Scryfall.
Defender (This creature can't attack.) At the beginning of your upkeep, this creature's base toughness becomes equal to 1 plus the number of creature cards in your graveyard. (This effect lasts indefinitely.)