I read this fanfiction a while ago, but now I can't find it. I'm hoping someone could help me.
So it was when Thor was taking Loki back to Asgard, I believe. Loki cast a spell right when that happened and suddenly Tony was in Loki's body. Tony spends most of his time trying to convince Thor and Odin that he actually isn't Loki, but they just think he's lying to get out of his punishment.
His punishment is that his eyesight is taken away, along with his hearing and I believe his speech as well. He can see if he really tries, since he also has Loki's magic. He's left in Loki's body to wander about Odin's palace, trying to figure out a way to get home and wondering what Loki is doing as him back on Earth.
Tony meets up with Jane Foster, who comes to visit Thor one time, and manages to convince her about his true identity. At one point, he turns into a bird and attempts to go through a portal that Jane is working on and almost dies from that. He uses some of his magic in front of Thor and Odin to show his true face for about a second and they finally realize their mistake. Eventually, he does get back to Earth.
Please, help! It was a really great fic, and I'd love to read it again.