Strixhaven Stadium is a rare Artifact card from Magic Online Promos (PRM), collector number 90326.
{T}: Add {C}. Put a point counter on this artifact. Whenever a creature deals combat damage to you, remove a point counter from this artifact. Whenever a creature you control deals combat damage to an opponent, put a point counter on this artifact. Then if it has ten or more point counters on it, remove them all and that player loses the game.