Now all I can think of is an AU where Odin kept Loki as a literal relic locked up with the other stolen Jotun things in the vault. One day, Thor and the Avengers finds a half-crazed Loki in there when researching the Tesseract.
“One day when we were kids, Loki turned himself into a snake, he knows I love snakes. So I picked it up to admire it, then he changed back into himself. He yelled “BLARGH ITS ME” and stabbed me”- Thor Ragnarok 2017