Ok my idea is two person got reincarnated into one body. Example twilight, twilight would still be there but she have two other souls. I got that idea from isekai tensei soudouki.
Hell, it could anyone then twilight.

It's an interesting idea, but in execution it often fails. Not that it's badly written per se, but the author often winds up unconsciously picking a favorite and forgetting about the other personalities/spirits/souls/whatever in the body.

7089554
So what woould it need to the execution to work? The two souls would need to be very different? Like one of them is a souls from the present, the other from Arthur era?

7089568
Mostly you just need to remember all parties involved, also make sure you draw specific boundaries for who has control of what aspect of the shared physical body. By this, I don't really mean, "Personality A gets control of the left arm, the right leg, and the left foot," or some similarly goofy arrangement, but more like, "Personality A is the one in the driver's seat, Personality B & C are more like Statler & Waldorf shouting from the box seats," or "Personality A is in charge during intimate situations, Personality B is an implanted survival A.I. that takes over when fight-or-flight instincts trigger an activation." Get creative, but don't have one personality take over where the other is established as the dominant for that area/domain/specialty/etc. UNLESS that unplanned, unexpected takeover would serve the story in some capacity and must be explicitely called out as, "Oh, s**t! This is personality A's job, not mine, WTF am I supposed to do?!" kinda thing.

7089767
I see, so who ponies have the more potential to change if do that when they are children? Exemple Fluttershy could become less shy but become greedy because of the other personalities. I think the one who could change themself and the world the most would be blueblood

7089791
Not exactly what I was saying, but absolutely. I actually had a similar idea myself a few years back that I sketched out a few scenes for (including a rather epic rap battle between Trixie and Luna) but eventually put on the back burner for reasons and eventually just dropped. In this fic, Trixie becomes the Princess of Friendship and Twilight becomes a Moondancer-like shut-in because both characters get someone else in their head influencing their actions.

7089800
Great, i just hope this can give ideas to people's, im really not good in English

7089882
Don't let that stop you, I've found that some of the best fanfics I've ever read are written by people for whom English is their second (or even 3rd or 4th) language.

7089889
Even so, i have difficulty to understand other people. You could said that my brain dont work like the other