There's yet to be an equivalent to Apocalypse Nigh covering ToAU and WotG.
Anyone who has done the missions should know the obvious bridge between the storylines, plus a little certain knighting ceremony from the epilogue avatar fights involving you-know-who (not voldemorte) is something they left hanging.
Odin's deal is that he loans power to those who desire justice... obviously in not so nice ways.
It's implied that the likes of Raogrimm and Lilith are only some of the many clients Odin dealt with. The Crystal War, across all alternate worlds, is just ripe for these pacts.
Cait Sith no doubt was heavily involved with "tampering" with these time-lines. Which just pisses Odin off because hey, without folks constantly suffering, he's outta a job! The more the multiverse is in turmoil, the better.
As his knight, Odin orders you to travel to an indeterminate point of time to eliminate this meddler. But you can't very well kill a friend(s), can you?
Wacky double-crossing shenanigans ensue, ending with Odin letting you off the job and Cait Sith thanking you by lending you a portion of her power.
Atomos is easier. It'd probably just go on another temper tantrum and you'll have to fix the problem by beating it up.