ok ok a few aus on this master post i'll link on pinned / whatever mobile accessible thing i make for him - sorted by in and out of fandom!
unbecoming! i can't get enough of this line of aus - essentially anyone other than jim getting the medal Without Resetting The World tm - jim retains knowledge of what's gone on, with mixed effects. i personally Love jim still functioning as a trollhunter, though more along the lines of main timeline toby & claire, and more along the lines of jack sturges. that, and potentially picking up the skathe hrun later.
jim escaping camelot and ending up in with either gunmar's army, or in dwoza properly - either or. just your Totally Normal Troll Guy With One Extra Finger On His Left Hand, totally doesn't also act like he's got human reactions too. maybe it's just from being locked up in camelot. as jim hesitates with a name, stumbling out 'ji...key... jiki!' and tries to disengage the conflict between humans and trolls; for better or worse. though he knows that gunmar must end up in the darklands, one way or another.
as a side tangent au to above- jim being lost to the darklands with and becoming the beast, replacing aaarrrgghh!! as gunmar's general once the shard corrupts him, but instead of losing his mind to the corrupted, he keeps his sanity for a while before going mad himself eventually. timey wimey bullshit can happen with a human jim stumbling upon him.
body swap - body swap magic is canon - is it a spell jim activates, or someone else does, or something in a trap that both characters trigger