How does Combat Damage Work with Undergrowth Champion?

Question

Undergrowth Champion is a 2/2 creature with an ability that reads:

If damage would be dealt to Undergrowth Champion while it has a +1/+1 counter on it, prevent that damage and remove a +1/+1 counter from Undergrowth Champion.

If Undergrowth Champion had 1 counter on it (making it a 3/3) and was in combat with another 3/3, how much damage would Undergrowth Champion deal? Would the counter being removed cause Undergrowth Champion to deal 2 damage? Or would the removal of the counter take place after damage amounts have been assigned? Would the opposing 3/3 live or die?

Answer 1

UC will deal three damage.

The key is that replacement and prevention effects change what you will perform. Necessarily, this happens before the replaced instructions are performed.

The event being replaced is

All combat damage that’s been assigned is dealt simultaneously.

In this case, the above means the following before prevention effects:

Simultaneously, UC deals 3 damage to the 3/3, and the 3/3 deals 3 damage to the UC.

But there's a prevention effect affecting the second half. Even if we naïvely apply apply the effect, the answer is clear

Simultaneously, UC deals 3 damage to the 3/3, and remove a +1/+1 counter from UC.

But as per 615.5, the additional part of the prevention effect is actually delayed, so we actually get

UC deals 3 damage to the 3/3, and then remove a +1/+1 counter from UC.

Either way, it's clear it does three damage.

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615.5. Some prevention effects also include an additional effect, which may refer to the amount of damage that was prevented. The prevention takes place at the time the original event would have happened; the rest of the effect takes place immediately afterward.

Answer 2

Barring any other ability considerations that alter timing (like First Strike), combat damage is applied simultaneously.

The Champion would deal 3 damage to it's opponent. The Champion would receive 3 damage from the opponent, which it is shielded from by the prevention effect, then the counter is removed. It looks like this falls under the following rule:

615.5. Some prevention effects also include an additional effect, which may refer to the amount of damage that was prevented. The prevention takes place at the time the original event would have happened; the rest of the effect takes place immediately afterward.

Answer 3

Damage is assigned first, per rule 510.1.

510.1. First, the active player announces how each attacking creature assigns its combat damage, then the defending player announces how each blocking creature assigns its combat damage. [...]

Damage is dealt second, per rule 510.2.

510.2. Second, all combat damage that’s been assigned is dealt simultaneously. [...]

Since Champion has a counter on it when damage is assigned, it assigns 3 damage.