So I had an idea to have another soul in the body of my character. She is a Halfling Rogue, Chaotic Neutral. And my plan is that she is going the Arcane Trickster path.
So the other soul is the reason she has the magical stuff. The hand is invisible, so it's more like she reaches out her hand and it flies toward her. Or that her tankard floats in the air, and hovers over to her as she drinks, and hovers back.  Stuff like that. But if this soul is ever gonna come up in the game, I need to have a personality for him/her. And I was hoping you guys had some ideas. Aloth & Iselmyr is a good example of this. But it doesn't need to be a hostile relationship. Anyway, Thanks in advance! ^^

I have a character like that in my campaign, we went the Venom path. in times of stress, she hears a voice to aid her and grants her magic over time she came to be able to talk to it all the time but when he is knocked to zero hp the other soul takes over with the same hp and fights using her body.

Most of the party in one of the games I GM had an extra soul hanging around in their bodies for a while, after they ate the souls of some villagers (before they realized that they could have instead used the souls to bring those villagers back from a state of zombie-alike-ism).

The way we handled it was each extra soul gave the eater some extra XP to represent the soul's experience, a small half-feat-like extra ability, proficiency in any ability check intrinsicly tied to that soul's experience, and some small role-play hints.

An example of one of the "Soul Cards" I gave out is:

Soul of the Broken Noble
Sildar Hallwinter, Human Male

 

Invigorating Meal. Upon consuming this soul, you feel an equisite rush of energy flow throughout your body. The feeling of sweet euphoria lasts one minute, then your body acclimates to the presence of the new soul in your body as the euphoric feeling begins to dissipate. Within six seconds of fully consuming the soul, your wounds close before your very eyes as your body converts the soul's energy to bring you up to full health. Your mind and any magic you possess is similarly invigorated, feeling as though you had a full rest.
You regain all lost hit points and are filled as if you had eaten a large meal. You also regain spent Hit Dice, up to a number of dice equal to half of your total number of them (minimum of one die). For example, if you have four Hit Dice, you regain up to two spent Hit Dice. If you have not consumed a soul in the past week, you also regain any uses of abilities, spells, or other traits that recharge upon a long rest.

Fragmented Memories. Upon consuming this soul, your mind becomes awash in fragments of the soul's memories, emotions, and knowledge.
Until you consume another soul, you can add your proficiency bonus to any ability check that you do not already add your proficiency bonus to and that the soul had intimate skill with or knowledge about.

Eternal Vigilance. Upon consuming this soul, you being to feel an unnatural dislike and fear of the underkin - goblins, bugbears, and their unnatural demonic kin make your skin shudder just by their presence. You are certain that they will backstab you at some point, and the only thing you can do is either prepare for it - or strike them first.
You keep your eyes and ears open at all times, and this enhanced state of vigilance means that lightly obscured areas don't impose disadvantage on your Wisdom (Perception) checks if you can both see and hear.
This trait lasts until you consume another soul.

You may recognize the Soul's name; this was a highly modified Lost Mines of Phandelver game.

The players acted out having these souls by altering their character's personalities while they were hosting the soul, occasionally having the soul's personality manifest more fully. An example of this is one character had a deep stutter, but his new soul had been a politician in life (the mayor of town), so occasionally when things were most appropriate (such as when speaking to the survivor's of Phandalen after the players accidentally/secretly burned the town to the ground) he'd lose the stutter and speak with much more confidence.

The Lawful Evil noble occasionally had minor conversations with his new Soul, but he did that with himself before he had the Soul as well, so it wasn't that different.

Primarily, the souls were integrated into the existing personalities and altered them.

Hope our experience helps you.

EDIT: Also, dying and being revived made the extra soul go away, since it wasn't fully tethered to the body. This includes losing all benefits of the card, including lowering their XP total, but not decreasing in level.

EDIT2: I've uploaded the cards I created, which might have some personality ideas you can borrow, to here.

Quote from LangyMD >>

Most of the party in one of the games I GM had an extra soul hanging around in their bodies for a while, after they ate the souls of some villagers (before they realized that they could have instead used the souls to bring those villagers back from a state of zombie-alike-ism).

The way we handled it was each extra soul gave the eater some extra XP to represent the soul's experience, a small half-feat-like extra ability, proficiency in any ability check intrinsicly tied to that soul's experience, and some small role-play hints.

An example of one of the "Soul Cards" I gave out is:

Soul of the Broken Noble
Sildar Hallwinter, Human Male

 

Invigorating Meal. Upon consuming this soul, you feel an equisite rush of energy flow throughout your body. The feeling of sweet euphoria lasts one minute, then your body acclimates to the presence of the new soul in your body as the euphoric feeling begins to dissipate. Within six seconds of fully consuming the soul, your wounds close before your very eyes as your body converts the soul's energy to bring you up to full health. Your mind and any magic you possess is similarly invigorated, feeling as though you had a full rest.
You regain all lost hit points and are filled as if you had eaten a large meal. You also regain spent Hit Dice, up to a number of dice equal to half of your total number of them (minimum of one die). For example, if you have four Hit Dice, you regain up to two spent Hit Dice. If you have not consumed a soul in the past week, you also regain any uses of abilities, spells, or other traits that recharge upon a long rest.

Fragmented Memories. Upon consuming this soul, your mind becomes awash in fragments of the soul's memories, emotions, and knowledge.
Until you consume another soul, you can add your proficiency bonus to any ability check that you do not already add your proficiency bonus to and that the soul had intimate skill with or knowledge about.

Eternal Vigilance. Upon consuming this soul, you being to feel an unnatural dislike and fear of the underkin - goblins, bugbears, and their unnatural demonic kin make your skin shudder just by their presence. You are certain that they will backstab you at some point, and the only thing you can do is either prepare for it - or strike them first.
You keep your eyes and ears open at all times, and this enhanced state of vigilance means that lightly obscured areas don't impose disadvantage on your Wisdom (Perception) checks if you can both see and hear.
This trait lasts until you consume another soul.

 

You may recognize the Soul's name; this was a highly modified Lost Mines of Phandelver game.

The players acted out having these souls by altering their character's personalities while they were hosting the soul, occasionally having the soul's personality manifest more fully. An example of this is one character had a deep stutter, but his new soul had been a politician in life (the mayor of town), so occasionally when things were most appropriate (such as when speaking to the survivor's of Phandalen after the players accidentally/secretly burned the town to the ground) he'd lose the stutter and speak with much more confidence.

The Lawful Evil noble occasionally had minor conversations with his new Soul, but he did that with himself before he had the Soul as well, so it wasn't that different.

Primarily, the souls were integrated into the existing personalities and altered them.

Hope our experience helps you.

EDIT: Also, dying and being revived made the extra soul go away, since it wasn't fully tethered to the body. This includes losing all benefits of the card, including lowering their XP total, but not decreasing in level.

EDIT2: I've uploaded the cards I created, which might have some personality ideas you can borrow, to here.

 That sounds great! Thank you! ^^

Quote from Estoy_Awesome >>

I have a character like that in my campaign, we went the Venom path. in times of stress, she hears a voice to aid her and grants her magic over time she came to be able to talk to it all the time but when he is knocked to zero hp the other soul takes over with the same hp and fights using her body.

 Mhh! I like the idea of the soul manifesting at certain points... ^^