okay. this is my first theory. becase english is not my native language you migh see here some gramer mistakes (evan my final exam in english was really good) or becasu i typing fast XD
melane was my second suspect ever. from the first time when we saw two red devil, i had the feeling that melanie is one of them. so this is my theory: nine reasons why melanie might be the twin AKA the other red devil
1. lets begin with the most obvious reason. right before the spray tan machine incident she said to chaenl "The next president of this house has to be to be willing to dance with the devil himself to keep this thing of ours going". and right before sonya's death the RD text her "wanna dance with the red devil?"
2. she didnt die. she was hurt and burnt. she couldnt stand. she was the perfect victim. but the red devil didnt killed her. why? maybe it was boone who want to frame chanel for the incident and make melanie hate the kappa.
3. before episode 6 we didn't knew how the red devil could appear from nowhere in the kappa's house. but in episode 6 we find out way: the red devil used the secrets tunnels. and only the presidents of the KKT know about the existence of the tunnels. melanie was the president before chanel.
4. when chanel and zayday were in the tunnels, they talked about the presidents during the years. right after this conversation the red devil attacked them. and we know it wasnt boone becaus boone didnt want to kill zayday. so the red dvil was the twin.
5. many of the deahts in show inculd the heads. people died because their heads: bean, sonya, tiffany, coney, caufiled, sam, roger, mr munch, jennifer and hester. well... melanie, as the former president was the HEAD of the kappa.
6. The motif of betrayal. many of the people who died involved with some betrayal. bean (she did the collage), sonya (wanted to leave), mandy (told to pete and grace what happend in 1995), sam (told three's secret), roger (was happy after his twin brother death), mr munch (cheated on cathy with feather), boone (want to kill gigi) and hester (her all plane was to betrey chanel and take her place). so maybe melanie see the spray tan machine as chanel's betrayal.
7. they showed to us the flashback. but way? i mean we didnt saw a flashback of the former dean's death or four's death. but we saw the spray tan incident. if we saw it, maybe it's important thing for the future of the show. and now we know that melnaie will be in the last two episodes.
8. why the twin wore the RD costume in the penthouse? boone didnt wore it and so gigi. why did the twin wore the costume? reason: her skin is burnt. she dont want to see it and she dont want anyone to see it. this is why she wore the costume when she killed boone.
9. why the twin killed her own twin brother? yes she want to protect gigi but boone didnt hold his kife. he couldnt do anything to gigi (he could strangel her but i dont think this is RD's style). the twin could stope him instad of kill him. what if boone did something really bad to his twin sister? did he burn her skin?