The Mightstone and Weakstone [The Brothers' War Prerelease Promos] Gateway 2008 this creature deals damage equal

this creature deals damage equal to that spell's mana value to target opponent

Set: Alpha Edition Type: Artifact Rarity: Uncommon Cost: {1} Whenever a player casts a green spell

Set: Aether Revolt Type: Artifact Creature — Construct Rarity: Rare Cost: {X}{X} Walking Ballista enters the battlefield with X +1/+1 counters on it

Set: Exodus Type: Instant Rarity: Common Cost: {B} As an additional cost to cast this spell

put a +1/+1 counter on Dirtcowl Wurm

The Mightstone and Weakstone [The Brothers' War Prerelease Promos] Gateway 2008 this creature deals damage equalSet: The Brothers' War Prerelease Promos Type: Legendary Artifact Powerstone Rarity: Rare Cost: {5} When The Mightstone and Weakstone enters the battlefield, choose one Draw two cards. Target creature gets 5 5 until end of turn. {T}: Add {C}{C}. This mana can't be spent to cast nonartifact spells. (Melds with Urza, Lord Protector.)