Had the decree that increases strength by armor amount and the one that gives armor upon finisher, so Stalker's Marked alone should've been able to kill a lot of things when paired with Teleport.

Scythe finishers usually have two hits. This bug might be caused by Molten Mettle triggering upon the first hit, while Marked will only trigger upon death. I remember playing Stalker before the update and even though the enemy would have died upon the first hit, the enemy would still be alive in time for the second hit (although the health bar is visibly barely empty). Marked would still take effect only after the second hit.

I haven't tested this thoroughly though since it's my first playthrough of Stalker since the update, that's why I haven't made a proper bug report in the forums. I'll try to see if not acquiring Molten Mettle would deal more damage or not. Let me know if you guys get the same results or not.