Rebirth potion x Feral child

[Laclale♪]

Feral Child says (or darkvision if you already had low-light vision)...

When transformed by Rebirth potion, ancestry changes causes feat and feature's overwrite.

If drinker had low-light as ancestry feature and lost because of potion's overwritten ancestry, what will happen for Feral Child's gaining vision?

[Luke Styer]

I can’t cite a rule, but my instinct is that whatever visual sense the character ended up with would be enhanced or not, independent of what visual sense the character had before.

[Laclale♪]

Same thing happenable for Magical experiment.

Here you can check rebirth potion.

[Cordell Kintner]

Your background would apply as if you always were the new ancestry.

[HammerJack]

Just as a general principle, there's no reason to think that "gain an ability, stop having the prerequisite to that ability and keep the ability" would ever be a thing. Regardless of whether the foundational ability is formally listed as a prerequisite or if it is like this "if you already have X gain Y instead" format.

[breithauptclan]

The Rebirth potion sounds like a justification for Extreme Retraining.

And Retraining action says:

Quote:

If you cease to meet the prerequisites for an ability due to retraining, you can't use that ability. You might need to retrain several abilities in sequence in order to get all the abilities you want.

In this particular case, the Feral Child background could apply to the new Ancestry, but would only give low-light vision if the new Ancestry doesn't provide that already.

Though I could also see using the Rebirth potion to change background as well - at least in the case of one that is giving physiological changes.