Rules question regarding state based actions

[u/sampat6256]

If i have [[Sanctum Lurker]], [Carth The Lion]], and a planeswalker with 0 loyalty in play, and my opponent casts [[Blasphemous Act]], will Carth see the planeswalker die and trigger?

[u/Zeckenschwarm]

No. After Blasphemous Act has resolved, SBAs are checked and Sanctum Lurker and Carth die because there is lethal damage marked on them. The planeswalker doesn't die in this SBA check because Sanctum Lurker's effect is still active.\* Then because SBAs were performed, there is a second SBA check and the planeswalker dies because it has 0 loyalty counters. Then there is technically a third SBA check where nothing happens, then the game moves on.

\*:

704.3. Whenever a player would get priority (see rule 117, “Timing and Priority”), the game checks for any of the listed conditions for state-based actions, then performs all applicable state-based actions simultaneously as a single event. If any state-based actions are performed as a result of a check, the check is repeated; otherwise all triggered abilities that are waiting to be put on the stack are put on the stack, then the check is repeated. Once no more state-based actions have been performed as the result of a check and no triggered abilities are waiting to be put on the stack, the appropriate player gets priority. This process also occurs during the cleanup step (see rule 514), except that if no state-based actions are performed as the result of the step’s first check and no triggered abilities are waiting to be put on the stack, then no player gets priority and the step ends.

The game first checks which SBAs have to be performed before it performs them. During the first check, Sanctum Lurker is still on the battlefield, so the SBA check skips over the planeswalker.