Sickening ShoalHow it works & interactions with other cards

Choosing Your Cost

When you cast Sickening Shoal, you have two choices for paying its costs. You can pay the mana cost of {X}{B}{B} using traditional mana sources. Alternatively, you may choose to exile a black card from your hand with a mana value exactly equal to X. If you choose the alternative cost, the value of X is determined by the mana value of the card you exile. For example, exiling a card with mana value 3 means X is 3, giving the target creature -3/-3.

Resolving the Weakness

Once the spell is cast and a target creature is chosen, it stays on the stack like any other instant. Upon resolution, the target creature receives -X/-X until the end of the current turn. Because this reduces toughness rather than dealing damage, it can effectively destroy creatures with Indestructible if their toughness reaches 0 or less. If the target becomes illegal before resolution, the entire spell is removed from the stack and does nothing.

Strategic Timing and Pitfalls

A common mistake is forgetting that you still must choose a value for X when paying with mana. If you pay {2}{B}{B}, X is 2. If you use the alternative cost, you cannot 'overpay' or 'underpay'—X must exactly match the exiled card's mana value. Since it is an Instant, it is best used during the combat phase to shrink an attacker or in response to a pump spell to ensure the creature's toughness drops to zero.

Interaction examples

The Free Removal Play

Dark Ritual

If you have Dark Ritual in your hand (mana value 1), you can cast Sickening Shoal by exiling Dark Ritual instead of paying {1}{B}{B}. This sets X to 1, giving a target creature -1/-1 until end of turn. This allows you to remove a small creature like a mana elf while remaining tapped out.

Setting Up the Perfect X

Vampiric Tutor

You can use Vampiric Tutor to search for a black card with a specific mana value that matches a threat on the board. If your opponent has a creature with 1 toughness, you search for any black card with mana value 1. You then draw it and exile it to Sickening Shoal to remove the threat for zero mana.