Seriously, I have no idea what happened. The player declared which Power was being used, and nobody had any idea how to narrate it, so we just moved on with the game and I think I stopped using that Power since it left gaps in the narrative.
A literal "failure of imagination," then. You left gaps in the narrative rather than either 1) accept how the power was described or 2) change it to something else.
This Power didn't give you anywhere near that level of detail. The best we could figure out was that maybe I gave the goblin a funny look, before it keeled over.
It's still a spell, so there's clearly going to be a little more to it...
Relevant bits:
"You have forged a pact with the dark beings that lurk in the shadows of the drow civilization. Spells of darkness, poison, madness, and spite fill your mind."
"Spiteful Glamor: The mere sight of you is anathema to your enemy."
As an arcane power, it's a spell. the use of spite in both places makes one aspect of it pretty clear, it involves that negative emotion. 'Glamour' is fey magic that changes appearances.
So, you use magic to make yourself look creepy in a way that messes with your target's mind. It does do psychic damage, which fits. It's presumably tailored to that individual, since it doesn't affect everyone looking at you. It had a greater effect on a target that hasn't been injured yet, too, which would indicate it's disquieting in a way that has less impact in the heat of battle. So fairly subtle creepy looking psychic spite.
It could be fun to narrate what the target sees differently each time, or you could just assume the same darksome appearance each time - or both. Just like you could actually come up with some vicious mockery each time you use Vicious Mockery, or describe how you cut down yet another orc with your sword differently each time - or not.
At least with a sword, you know that you cut the enemy. You might have slashed or stabbed it, in any number of ways - you might have hit armor, or skin - but you definitely applied the sword directly to the goblin and then the goblin died.
Maybe. Or maybe the final blow that killed the goblin was a Reaping Strike, and you actually caved in his little goblin noggin with the pommel. Or pulled the strike and only KO'd him. You have a fair bit of 'narrative power,' even there.
It's an issue of degree to the abstraction.
You can make it a lesser degree of abstraction if you choose fluff that more closely maps to the mechanics (in your view thereof).