Rockslide Elemental vs. Tephraderm

Consider these questions:

1. A Rockslide Elemental with four +1/+1 counters (making it thus 5/5) attacks, and a Tephraderm blocks it. Does the Elemental survive?
2. Would it make any difference if it were the Tephraderm that's attacking and the Elemental that's blocking?

Since the Elemental has first strike, it deals 5 damage to Tephraderm in the first strike combat step, which is lethal damage. Tephraderm does not deal combat damage (because it has no first strike), but its ability triggers, which deals 5 damage back to the Elemental when it resolves. When Tephraderm dies due to the lethal damage, Elemental's ability triggers which, when it resolves, gives it an additional +1/+1 counter.

Thus the question is: Which happens first, Tephraderm's ability dealing 5 damage to Elemental (which would then die), or the latter getting a +1/+1 counter (saving it)?

The answer can be quite tricky to figure out if one doesn't know the finest details of the game's rules.

One could naively think that since the Elemental deals damage first, Tephraderm therefore dies first and Elemental gets its additional counter, saving it. But then when one thinks a bit more, one realizes that at the exact moment that the Elemental deals combat damage to Tephraderm, the latter's ability triggers, and would deal damage back to the Elemental before its +1/+1 ability has the chance of triggering... And the train of thought can continue further from there, creating a chicken-and-egg problem.

A more experienced player can guess, correctly, that both abilities go onto the stack in APNAP order, but may not be able to tell precisely why.

("APNAP" order, or "active player, non-active player" order means that if two effects, controlled by different players, are trying to enter the stack at the same time, the effect of the active player goes to the stack first, and the non-active player then. They then resolve in reverse order, ie. the effect of the non-active player resolves first.)

So the core question here is when exactly does Tephraderm die. As you may know, and as I detailed in my previous blog post, a creature is destroyed from lethal damage only the next time that state-based actions are checked (which is different from eg. effects that say "destroy," which destroy the creature immediately.) Therefore the core question becomes: When exactly are SBA's checked here?

More precisely, the difficult question is: When Elemental deals its combat damage to Tephraderm, triggering the latter's ability, are state-based actions checked before or after said ability enters the stack?

This makes a big difference because if SBA's are checked only after the ability enters the stack, then the order of the two abilities is always the same. However, if they are checked before, then the two abilities are actually trying to enter the stack at the same time, and APNAP order applies.

The correct answer is that yes, state-based actions are checked between an ability triggering and it entering the stack. This means that when Tephraderm is dealt damage and its ability therefore triggers, before said ability enters the stack SBA's are checked and Tephraderm dies (due to lethal damage) triggering Elemental's ability. Therefore the two abilities are trying to enter the stack at the same time.

Therefore the correct answers to the questions at the beginning are:

1. No, Rockslide Elemental does not survive. This is because its ability is controlled by the active player (because the Elemental is attacking, meaning that it's being controlled by the active player) and therefore enters the stack first, and would therefore resolve after the Tephraderm's ability, which kills the Elemental before it gets the additional +1/+1 counter.
2. Yes, it makes a difference. If Elemental is defending, it means that it's being controlled by the non-active player, and therefore its ability enters the stack last, thus resolving first, and giving it an additional +1/+1 counter before Tephraderm's ability deals it 5 damage.

This is a detailed sequence of events:

• Rockslide Elemental assigns 5 damage to Tephraderm in the first-strike combat damage step.
• Tephraderm's ability triggers (but does not yet enter the stack.)
• State-based actions are checked, which cause Tephraderm to be destroyed due to lethal damage. Tephraderm is immediately put into its owner's graveyard.
• Rockslide Elemental's ability triggers due to Tephraderm dying (but does not yet enter the stack.)
• State-based actions are checked, but nothing special happens.
• The two abilities enter the stack in APNAP order. SBA's are checked, nothing happens.
• If Rockslide was attacking, it means Tephraderm's ability resolves first, assigning 5 damage to Rockslide. SBA's are checked and Rockslide is destroyed. Its own ability then resolves and fizzles.
• If Rockslide was blocking, then its ability resolves first, giving it an additional +1/+1 counter. Then Tephraderm's ability resolves assigning it 5 damage. However, since Rockslide is now 6/6, it survives.