This might be Monster Falls as well, so...

Basically, Loki is imprisoned. He wishes to be let free, and his thoughts fly across Midgard, where they reach a certain Illuminacho in Oregon. The  Illuminacho in question leaps dimensions or something to get to Asgard. As Bill is a trillion-year-old Dream Demon, he appears to Loki in the mindscape to have a cup of tea. Where a cup is a handshake, of is covered in, and tea is blue fire. AKA, a deal.
Loki, not having previously known about Bill, accepts. Gee, what could go wrong?

Meanwhile, Thor learns of Loki's escape. He goes to Avengers, where he is met with Stanford talking to Tony about something. Stanford is fangirling a little over Bruce, while Tony is fangirling a little over Stanford. Stanford talks about how this guy named Bill has magic powers and escaped custody in his town(because he does NOT want to reveal to the Avengers, and by extent, SHIELD, that Bill is actually a literal demon nor that Gravity Falls, Oregon has magic and stuff). Thor realizes that one of the guards talked about everything going gray, which is what Stanford talks about as one aspect of Bill's 'magic'. Thor speaks up, Stanford realizes Bill and Loki are working together. He rushes back to Gravity Falls to get aid.

The *extremely simplified* introduction to this story!
I WILL MOST LIKELY BE DOING THIS