Boon-Bringer Valkyrie - Promo Pack (PMOM) from March of the Machine, available at 401 Games Canada.

• Rarity: Rare
• Finish: Normal
• Artist: Heonhwa
• Card Text:
  Backup 1 (When this creature enters the battlefield, 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