Chaotic Synapse's

Two souls inhabiting the same body while possible has some Interesting side effects. Being the soul that originally inhabits the body, the main soul is primarily in control. However, in times of extreme duress the other soul can seize control (upon a failed Con save of 16) as a result of the minds instability and a complete swap occurs. The soul that seizes control in this moment changes the body to fit that of the soul in control. This also enables the bearer to have a sort of "second-life" as when one soul goes unconscious the other gains full control of the body. This has some downsides as it results in gaining 2 instantaneous levels of exhaustion (upon a failed Con save of 19) as a result of the abrupt swap.