As the title says, I'm looking for an ASU AU where Clark's amnesia is permanent due to a mix of kryptonite & some kind of nerve gas that Lex Labs hides in his air supply when he leaves to take on Nightfall.

Any help is appreciated, I'd really like to re-read it if I could just remember the title.

Hi Endelda!

This sounds like bobbart's Skyfall.

Michael

Hi Endelda,
I think you are talking about "When the Sky falls" by Bob Bartholomew. The amnesia is mostly permanent except for some small Bytes due to a pison Lex put into Clark's stuff.
There is also a Sequel to this caled "After Nightfall" or so. You find both stories in the Archive.

That's exactly the story I was thinking of, thank you both!