Corrosive MentorHow it works & interactions with other cards

Understanding Wither

Wither is a keyword that changes how damage is dealt to creatures. Instead of marking damage that clears at the end of the turn, a creature with wither deals damage in the form of -1/-1 counters. This effectively shrinks the power and toughness of the blocking or blocked creature forever. It is important to note that wither does not change how damage is dealt to players or planeswalkers; they still lose life or loyalty as normal.

Step-by-Step Resolution

First, Corrosive Mentor must be on the battlefield for its static ability to function. Any creature you control that has the color black gains the wither ability immediately. When a black creature you control deals damage to another creature—whether through combat or an effect—the game checks for wither. Instead of the damage being marked on the recipient, the game places a number of -1/-1 counters on that creature equal to the damage dealt.

Common Mistakes

A common misconception is that Corrosive Mentor gives itself wither; since it is a black creature, it indeed benefits from its own ability. Another mistake is assuming wither functions like deathtouch. Wither requires the damage to be high enough to actually reduce a creature's toughness to zero to kill it, though the permanent reduction in power often makes the target useless even if it survives. Finally, remember that color matters: colorless creatures like artifacts do not gain wither from this ability unless another effect makes them black.

When to Play It

Corrosive Mentor is most effective in decks that rely on winning combat through attrition. It is excellent against decks with high-toughness creatures or creatures with indestructible, as -1/-1 counters can still kill a creature with indestructible if its toughness reaches zero. It also synergizes well with effects that trigger when counters are placed on creatures.

Interaction examples

Wither and Colorless Creatures

Solemn Simulacrum

If you control both cards and Solemn Simulacrum blocks an opponent's creature, it will deal normal damage. Because Solemn Simulacrum is a colorless artifact creature, it does not receive the wither bonus from Corrosive Mentor. The opposing creature will have damage marked on it until the end of the turn, but no -1/-1 counters will be placed.

Elemental Synergies

Roaming Throne

If you play Roaming Throne and choose 'Elemental', it becomes an Elemental in addition to its other types. However, Roaming Throne is still colorless. Even though it shares a type with Corrosive Mentor, it will not gain wither because it is not a black creature. Furthermore, Corrosive Mentor's ability is a static ability, not a triggered ability, so Roaming Throne's doubling effect does not apply here.

Combat with Corrosive Mentor

Corrosive Mentor attacks and is blocked by a 3/3 creature. As a 1/3 black creature, Corrosive Mentor deals 1 damage. Because it has wither, it places one -1/-1 counter on the 3/3 blocker. The blocker is now permanently a 2/2 creature. Meanwhile, Corrosive Mentor takes 3 normal damage from the blocker and is destroyed, as wither does not protect the source from incoming damage.