Boon-Bringer Valkyrie is a rare Creature — Angel Warrior card from March of the Machine (MOM), collector number 343. Current market price: $0.45 (foil $0.45), 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