Might of Old Krosa is a uncommon Instant card from Modern Masters 2017 (MM3), collector number 130. Current market price: $0.26 (foil $0.61), TCGplayer market prices via Scryfall.
Target creature gets +2/+2 until end of turn. If you cast this spell during your main phase, that creature gets +4/+4 until end of turn instead.