Undergrowth is a common Instant card from Alliances (ALL), collector number 102a. Current market price: $0.23, TCGplayer market prices via Scryfall.
As an additional cost to cast this spell, you may pay {2}{R}. Prevent all combat damage that would be dealt this turn. If this spell's additional cost was paid, this effect doesn't affect combat damage that would be dealt by red creatures.