It's closest to Wail of the Banshee (multitarget death spell), but that's a 9th level spell specifically dedicated for that effect.
Were it my game, I'd rule a Wish for killing someone is basically a Wish that's emulating Finger of Death or similar. But it's not, so...alrighty.
My question is this:
In the Astral Plane magic is enhanced. Does this apply only to spellcasting, or does it also apply to Spell-Like Abilities?
EDIT - Nevermind; I looked up the Astral plane and yes, it seems SLA's are affected as well.
...groovy.
*coughs*
I, uh, take it back about Thorn's performance in combat being lackluster.
I just wasn't using her correctly before.
Now I understand.