just rewatched, it doesn’t appear the tip of the stake moves at all after Eric grabs Russel. It is kinda odd that Eric’s hand looks like it’s all the way against Russel’s body (like the stake is already driven in) when we first see Eric holding Russel. So either… 1) he staked him right as he grabbed him, and it just took a few seconds, then some glowing followed by melting, for him to die from the staking (i guess since he’s so old?) or 2) Eric didn’t stake him at all. Was about to until he started glowing (Eric’s expression appeared a bit confused), melted, then exploded. Meaning that it took a few seconds for the Fairy energy to well up and kill him. Perhaps he could withstand it for a little while due to all the powerful fairy blood he’d just drunk (like it gives them temporary immunity to sunlight), but then once that wore off (which we know it does), he died from the light. This seems a bit more likely then the first scenario. And I agree that for the death of a multi-season-spanning arch-villain, it should have been clearer.