Cosmium BlastHow it works & interactions with other cards

Understanding the Conditions

Cosmium Blast can only target a creature that is currently in a state of attacking or blocking. A creature is considered an 'attacking creature' from the moment it is declared as an attacker in the Declare Attackers step until the end of the combat phase. Similarly, a 'blocking creature' remains such from the moment it is declared as a blocker until the combat phase concludes.

How it Resolves Step by Step

First, you must wait for the combat phase to begin. Once your opponent has declared attackers or you have declared blockers, you cast Cosmium Blast by paying its mana cost and selecting a legal target. Upon resolution, the spell checks if the target is still an attacking or blocking creature. If it is, Cosmium Blast deals 4 damage to it. If this damage is equal to or greater than the creature's toughness, it is destroyed and moved to the graveyard.

Timing and Common Mistakes

The most common mistake is trying to use Cosmium Blast outside of combat; you cannot use it on a creature just because it attacked earlier in the turn once the combat phase has ended. Additionally, if the target is removed from combat (for example, by a spell that exiles it or a 'remove from combat' effect) before Cosmium Blast resolves, the spell will fail to resolve because its target is no longer legal.

Strategic Placement

While white often uses exile effects like Swords to Plowshares, Cosmium Blast is more restrictive but excellent for handling threats in aggressive environments. It is best played after blockers are declared but before damage is dealt to save your own creatures, or after damage is dealt to finish off a high-toughness blocker that survived combat.

Interaction examples

Exile vs Damage

Swords to Plowshares

If your opponent attacks with a 4/4 creature, you can choose to exile it permanently with Swords to Plowshares at any time. However, if you choose to use Cosmium Blast, you must wait until it is declared as an attacker. If the opponent has a way to give the creature indestructible, Cosmium Blast will deal its 4 damage but fail to destroy it, whereas Swords to Plowshares would still exile it.

Responding to Targeted Exile

Path to Exile

Suppose you cast Cosmium Blast on an attacking creature. In response, the opponent casts Path to Exile on their own creature to save it from the damage and search for a land. Because Path to Exile resolves first, the creature is exiled. When Cosmium Blast tries to resolve, its target is missing, and the spell is removed from the stack with no effect.