The ability of Ashiok's Reaper was not triggered
I attacked with Ashiok's Reaper enchanted by the ability of Syr Armont, the Redeemer. Ashiok's Reaper was blocked by Aquatic Alchemist and the opponent cast Sugar Rush to Aquatic Alchemist. Then both creatures are defeated but the ability of Ashiok's Reaper was not triggered.
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[Deleted User] commented
That's because the creatures went to the graveyard a teeny tine bit earlier than the enchantment. So there was no Reaper to see the enchantment hit the graveryard.
Longer explanation:
State based actions see both creatures with lethal damage marked, so they get destroyed. No other state based actions has to be performed at this point. Then a recheck of state based actions occurs, because something had to be cleared up. Now state based actions see an aura that is not attached to anything, and that aura is put into the graveyard. There is no Reaper to see that event nor is there a Reaper going to the graveyard at this same time.