Overkill is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Target creature gets -0/-9999 until end of turn.

Complete guide

Overkill is a unique and flavorful instant that takes the concept of a debuff to an extreme level. By providing a massive reduction to a creature's toughness, it ensures that even the most resilient threats on the battlefield are efficiently dealt with.

What It Does

Overkill is a black instant costing two generic and one black mana. Its sole purpose is to reduce a target creature's toughness by 9999 until the end of the turn. In Magic: The Gathering, a creature with toughness of 0 or less is put into its owner's graveyard as a state-based action. Because this card reduces toughness rather than dealing damage, it bypasses keywords like Indestructible.

How It Resolves

When you cast Overkill, you choose a legal target creature. Upon resolution, the creature's toughness is modified by -9999. Even if the creature has high natural toughness or significant buffs, its total toughness will almost certainly drop below zero. Once the spell finishes resolving, the game checks state-based actions; seeing a creature with zero or less toughness, the game moves that creature directly to the graveyard.

Common Mistakes

A common mistake is assuming this card deals damage. Since it is a toughness reduction, it does not trigger abilities that care about damage being dealt, nor can the reduction be 'prevented' like damage. Additionally, remember that the effect only lasts until the end of the turn. If a creature somehow survives having its toughness reduced (which is unlikely given the magnitude), it will regain its original stats during the cleanup step.

When to Play It

Overkill is best used to remove high-toughness creatures that your opponent relies on for blocking or utility. Because it is an instant, you can use it during an opponent's turn to disrupt their strategy or during your own combat phase to remove a blocker. It is particularly effective against creatures with Indestructible, as those creatures cannot be destroyed by damage or 'destroy' effects, but they still die to zero toughness.

Interaction examples

Bypassing Sacrifice Costs

Deadly Dispute

If your opponent attempts to cast Deadly Dispute by sacrificing a creature as an additional cost, you cannot use Overkill to 'kill' that creature in response to prevent the sacrifice. The sacrifice happens as a cost to cast the spell, so the creature is gone before you get priority to cast Overkill. However, if they target a creature with a different spell, you can use Overkill to remove that creature first.

Redundancy in Removal

Deadly Rollick

In a situation where you face a creature that cannot be exiled, such as one with protection from white/blue or specific hexproof abilities, Overkill provides a different avenue of removal compared to Deadly Rollick. While Deadly Rollick exiles, Overkill reduces toughness. If you have both in hand, you can choose the one that bypasses your opponent's specific keyword defenses.

Guide written with AI from the official text and rulings. Official English text prevails.