Roar of Jukai is a common Instant — Arcane card from Betrayers of Kamigawa (BOK), collector number 140. Current market price: $0.08 (foil $0.60), TCGplayer market prices via Scryfall.
If you control a Forest, each blocked creature gets +2/+2 until end of turn. Splice onto Arcane—An opponent gains 5 life. (As you cast an Arcane spell, you may reveal this card from your hand and pay its splice cost. If you do, add this card's effects to that spell.)