Archangel Avacyn // Avacyn, the Purifier

Archangel Avacyn's delayed triggered ability won't cause it to transform back into Archangel Avacyn if it has already transformed into Avacyn, the Purifier, perhaps because several creatures died in one turn.

Archangel Avacyn's delayed triggered ability triggers at the beginning of the next upkeep regardless of whose turn it is.