Astral Cornucopia (Retro Schematic) (Serial Numbered) [The Brothers' War Retro Artifacts] Dark Ascension Promos Does 30 damage plus 20

Does 30 damage plus 20 more damage for each W Energy attached to Dark Blastoise but not used to pay for this attack

Set: Limited Edition Alpha Type: Enchantment Rarity: Common Cost: {2}{B}{B} At the beginning of the end step

Set: Battle for Zendikar Prerelease Promos Type: Creature — Cat Beast Rarity: Rare Cost: {4}{W}{W} Vigilance

You can't add more than 40 damage in this way

Astral Cornucopia (Retro Schematic) (Serial Numbered) [The Brothers' War Retro Artifacts] Dark Ascension Promos Does 30 damage plus 20Set: The Brothers' War Retro Artifacts Type: Artifact Rarity: Rare Cost: {X}{X}{X} Astral Cornucopia enters the battlefield with X charge counters on it. {T}: Choose a color. Add one mana of that color for each charge counter on Astral Cornucopia.