Bloodhill Bastion is a common Plane — Equilor card from Planechase 2012 Planes (OPC2), collector number 12. Current market price: $0.99, TCGplayer market prices via Scryfall.
Whenever a creature enters, it gains double strike and haste until end of turn. Whenever chaos ensues, exile target nontoken creature you control, then return it to the battlefield under your control.