Cephalid Coliseum is a uncommon Land card from Tarkir: Dragonstorm Commander (TDC), collector number 349. Current market price: $0.33, TCGplayer market prices via Scryfall.
{T}: Add {U}. This land deals 1 damage to you. Threshold — {U}, {T}, Sacrifice this land: Target player draws three cards, then discards three cards. Activate only if there are seven or more cards in your graveyard.