how do you handle permanent transformation?

[oninowon]

In Stargate Atlantis, there was a species that posed a threat to Atlantis called the Wraith. They can be simply described as space vampires. If I wanted to emulate this in game terms, how would I go about it? Would I go about building it using character themes or by archetypes?

[John Mangrum]

Are you asking for advice on how to create a Wraith PC in Starfinder or just more generally how to "convert" a living PC into undead?

[Metaphysician]

I would treat permanent transformations as an Affliction, most likely a Disease. Permanently changing the species of a victim would be its end-state, instead of death. Assuming it isn't purely a plot matter, anyway: if the transformation can only occur voluntarily, or only under circumstances where someone is already dead, then you don't need mechanics, only plot logic.

That said, if the new species they are being transformed into wouldn't be a valid PC race, then I would strongly suggest treating it like death anyway: if the character suddenly gains the equivalent of several levels worth of oomph, they shouldn't remain under the control of the player.

[Belabras]

I'd use the Corruption rules. which does what Metaphysician is describing.