I had thought that replacements *were* Sues that had made themselves look like a canon character. I seem to recall that being the case in the Original Series; Jay and Acacia had to go find the real character after killing the replacement.

I have had characters in Bad Slash be replacements. For instance: Holmes is an insecure priest who is victimized by a serial stalker/rapist Watson. Rape is love is the name of the game. Neither character even remotely resembled their canonical selves. I considered these guys to be replacements.

In another mission, Watson is a sociopathic serial killer, who has been murdering people (in as bloody and gruesome manner possible) for the last ten years, yet Holmes never noticed--Lestrade figured it out first! Holmes is taken down by Watson, but then tracks him to the US (not yet a replacement, due to certain in-character happenings in the stroy, just badly OOC overall). When Holmes contacts Watson it is to join Watson in the killings, which then incites the canonically asexual Holmes into a sexual frenzy. At that point he's a replacement.

In a third mission, Holmes is displaying infantile behavior, is unobservant, unintelligent, physically incapable of defending himself, and uninterested in solving crime. At the same time, he is captured, tortured (the plot was to eventually involve box jelly fish), Watson is a jerk to him, and several other things happened that just basically ruined his day. Watson dumps Mary, is a terrible, insensitive, brutal, abusive jerk, and an incompetent doctor. I was entirely ready to kill them both as Stus, but the story just didn't quite support either of them being Stus. In the end, I had Holmes at 99.99% OOC and Watson at 97.67% OOC.

In all those missions, the canons were terribly out of character. If I were doing the same missions now, I might make different decisions. In each case, I thought about it, and made the decision based on what felt right for the story and the mission. Yes, you have to have characters that are way out of character before you can justify killing them, but you can also have characters that are way OOC and not kill them. In the end it's a judgement call.

Ok thanks

If they wish to hurt someone then that would make it easy for the whatever(in fiction I mean, I know that hypnotism isn't this strong in real life) because they could just make the person think that everything going on was happening in their imagination, but it wouldn't work for the purposes of making someone kill the person they love.

You can't "force" someone to do something through hypnotization, it's called power of suggestion for a reason. Once you've forced them to do something against their will, then it's gone from hypnotization to outright mind control.