Marsh GasHow it works & interactions with other cards

What It Does

Marsh Gas is a global effect that applies a -2/-0 modifier to all creatures currently on the battlefield. Because it affects 'all creatures,' it does not target, meaning it bypasses keywords like Hexproof, Ward, or Protection from Black. It only affects creatures that are present on the battlefield at the moment the spell resolves.

How It Resolves Step by Step

First, you cast Marsh Gas by paying one black mana. Once the spell resolves, the game checks every permanent on the battlefield to see if it has the 'creature' type. Every creature identified at that specific moment receives the -2/-0 penalty until the end of the current turn. Creatures that enter the battlefield later in the turn will not be affected by this specific resolution of Marsh Gas.

Common Mistakes

A common mistake is thinking Marsh Gas lowers toughness; it only affects power, so it will not destroy creatures with low health on its own. Additionally, players often forget that the set of creatures affected is locked in when the spell resolves. If your opponent plays a creature spell after Marsh Gas has finished resolving, that new creature will enter with its full power intact.

When to Play It

The best time to cast Marsh Gas is during your opponent's Declare Attackers step. By reducing the power of their entire army before damage is dealt, you can safely block with your own creatures or simply take significantly less damage to your life total. It is also an excellent response to decks that generate many small 1/1 or 2/2 tokens.

Interaction examples

Fast Mana Defense

Dark Ritual

If your opponent is attacking you with multiple creatures and you have no mana untapped, you can cast Dark Ritual to add three black mana to your pool. You then spend one of that mana to cast Marsh Gas, reducing the power of all attackers by 2 and leaving you with two black mana remaining for other spells.

Searching for a Solution

Vampiric Tutor

During your opponent's upkeep, you can cast Vampiric Tutor to search your library for Marsh Gas and put it on top of your deck. Once you draw it during your turn, you are prepared to cast it later that round to survive a large incoming attack that would have otherwise been lethal.

Neutralizing Small Threats

If your opponent controls three 2/2 creatures, casting Marsh Gas will turn them all into 0/2 creatures until the end of the turn. This allows you to block them with your own creatures without fear of your blockers taking any damage, or simply ignore the attack entirely as they deal 0 total damage.