Dude, I just thought of something here.
Well, everyone knows that after Color manages to save Killer, with him motivating him to work on himself to become a better person, Nightmare loses one of his most loyal henchmen.
But, as we know, Nightmare wouldn't give up easily on that. So, what would he do? He would try to get a version of Killer from another timeline, because, like, he can get as many Killers as he wants, even make an army of them.
And with what Nightmare did, the people from the AUs that were attacked by him would see this version of Killer acting, and the people from the Omega Timeline would know about it and think that Killer tricked them and is secretly working for Nightmare. The Star Sanses might even be alarmed about this, wanting to interrogate Killer before any action.
Killer would be bombarded with accusations and insults until they found out what was really going on. Of course, Color would still be by his side trying to defend and comfort him.
I also like to imagine the two Killers facing off at some point, with Killer (the one saved by Color) trying to tell him to stop, convincing him that what he's doing won't lead to anything and that he can be better than this. He wouldn't judge him, because he is, like, what he was in the past.
I even thought that the Killer could redeem this other Killer, but I think a more realistic scenario would be for Nightmare to kill this Killer the moment he decided to go to the Omega Timeline with him.
Wouldn’t be surprised if the omega timeline or those aware of the the multiverse knows that nightmare tends to replace killers.
Apparently in Dreamtale’s canon, killer was replaced like 3 times—either before or after the one in something new. Wonder if some people don’t give any killers that get free a chance not because they don’t believe he can change or be trusted, but because they don’t believe this one will live long anyway and then nightmare will replace him with a new one or something.