Boon-Bringer Valkyrie is a rare Creature — Angel Warrior card from March of the Machine Promos (PMOM), collector number 9p. Current market price: $0.55 (foil $0.51), TCGplayer market prices via Scryfall.
Backup 1 (When this creature enters, put a +1/+1 counter on target creature. If that's another creature, it gains the following abilities until end of turn.) Flying, first strike, lifelink