Dark Valkyria (Mosaic Rare) (BP02-EN064) - Battle Pack 2: War of the Giants Unlimited

This card is treated as a Normal Monster while face-up on the field or in the Graveyard. While this card is face-up on the field, you can Normal Summon it to have it become an Effect Monster with this effect. // * Once, while this card is face-up on the field: You can place 1 Spell Counter on it. This card gains 300 ATK for each Spell Counter on it. You can remove 1 Spell Counter from this card, then target 1 monster on the field; destroy that target.