What happens if a psion manifests fusion and the fusion true mind switches?

[Zephonim]

Also

What happens if you manifest fission and then you and your duplicate true mind switch into two seperate bodies?

[Segev]

The rules don't really cover this. There are a number of ways you could interpret it, and the core of these issues also comes into the tactics people like to use with astral seed and fusion to permanently acquire the powers and abilities of those with whom they've fused.

So the ultimate answer is: whatever the DM wants to rule. However, you came here for analysis, and maybe DMs would like some suggestions, so...

Let's say we have Sam the Psion, Fred the Fighter, and Alice the Aaraockra.

Sam fuses with Fred, and true mind switches with Alice because Samred wants the bird-person body.
Possibility 1 (the boring, but probably most balanced one): When the fusion ends, Samred's body splits into Sam and Fred, Alice remains in Sam's body, and Fred snaps back to his body.
Possibility 2: Samred's fused mind and non-body powers stay in Alice's body after the fusion ends, and Samred's body splits into Sam and Fred, leaving Alice in Sam's body and Fred's body a mindless husk.
Alternate fate for Samred's mind: Sam and Fred split, but are both in Alice's body, acting kind-of like a schism-affected psion.
Possibility 3: As P2, but Alice's mind splits into two, so now there are two Alices, one in Sam's body, and one in Fred's.
Sam fissions into two, then true mind switches with both Alice and Fred (one Sam per switch). This leaves one Sam in control of Fred's body, one Sam in control of Alice's body, and Fred and Alice each in a copy of Sam's body.
Possibility 1: When the fission ends, the two Sams are forced into one body, and one of the two (possibly determined by a contested Charisma check) stays stuck in Sam's body, while the other swaps back to his or her own. Sam is left only in the body of the one who didn't get forced back into their original body.
Possibility 2: When the fission ends, Alice and Fred are affected as per a schismed psion living in Sam's body, while two copies of Sam control Fred and Alice's original bodies. This is akin to having used mind seed on one of them and true mind switching with the other.
Possibility 3: When the fission ends, Fred and Alice's original bodies merge as per fusion, leaving just Sam in control, and either the dual Sam-bodies stay split (with Alice and Fred in each), or they merge as per P2.

This is probably not exhaustive, but I hope it at least gives some ideas.

[Malroth]

++?????++ Out of Cheese Error. Redo From Start.

[PhantasyPen]

Ya got any ham to go with that cheese laddie?

[Calthropstu]

For the fusion true mindswitching:
Going by raw, the fused minds split at the end of the duration. There are 3 bodies and 3 minds. Whichever side had true mindswitch as a power stays in the mindswitched body. The mindswitched mind gains that person's body and the third goes back to their original body.

For fission, the main body remains as well as the main mind. Simple mindswitch there. The secondary mind ceases to exist because the energies sustaining it disappear. The body it switched into becomes a mindless husk.
The temporary body switched from disappears, killing the mind that was switched into it. You suffer the effects of being unable to refuse with your clone.

[Necroticplague]

Considering that Fusion and Fission are temporary effects, I'd personally rule that they work in a straightforward manner while the temporary affect is up, and then the 'end state' is as if they had never been manifested once they're done. Makes it at least easier to deal with, if a bit odd logically for the second example.

[Calthropstu]

Considering that Fusion and Fission are temporary effects, I'd personally rule that they work in a straightforward manner while the temporary affect is up, and then the 'end state' is as if they had never been manifested once they're done. Makes it at least easier to deal with, if a bit odd logically for the second example.

The problem lies with true mind switch, which is NOT a temporary effect. Fission and fusion, while temporary, get wonky with permanent mind affecting (or even longer duration temporary) effects thrown in. Ie: what happens if a fusion manifests fission just before the fusion wears off? Or a fission similarly manifests fusion? Or what happens if a fusion gets dominated?

[Venger]

The problem lies with true mind switch, which is NOT a temporary effect. Fission and fusion, while temporary, get wonky with permanent mind affecting (or even longer duration temporary) effects thrown in. Ie: what happens if a fusion manifests fission just before the fusion wears off? Or a fission similarly manifests fusion? Or what happens if a fusion gets dominated?

You can't use fission as a fused creature. You can't use fusion on a fissioned creature. Domination affects a fused being normally.

[Calthropstu]

You can't use fission as a fused creature. You can't use fusion on a fissioned creature. Domination affects a fused being normally.

Domination affects a fused creature normally, yes. But what happens when fusion ends? Are both people dominated still? Does the domination simply end because it was the fused character?, not the individual parts? Do hey get new saving throws?