Prahv is a common Plane — Ravnica card from Planechase Anthology Planes (OPCA), collector number 64. Current market price: $4.25, TCGplayer market prices via Scryfall.
If you cast a spell this turn, you can't attack with creatures. If you attacked with creatures this turn, you can't cast spells. Whenever chaos ensues, you gain life equal to the number of cards in your hand.