I know y'all don't know about this, but I had a homebrew ancestry for Gaia that was tiefling, aasimar, and dhampir rolled into one, because The Doom (artificial god of destruction) liked to amalgamate things while it corrupted them.
Pathfinder 2e has Tiefling, Aasimar, and Dhampir as versatile heritages so you can be a human/elf/dwarf of all those things. If I can call these outsider/undead folk Doomspawn and just let them take feats from each other, then my work on them is done. Doomspawn exist without much work.
Now I have a spare spot in my list of "Doomed" ancestries. I already have a twist on two fan favorites: Orcs represented as Orkhal and Goblins represented as Hobbelings- each with new lore and society to match the history of the world. I believe another fan favorite to fill this third spot could be Slimes.
Allow me to introduce you to The Coalesced! Like Halflings and Primordials, and even The Other World, The Coalesced came to be out of debris in contact with The Prime Element. As a result of the corruption of The Doom and the destruction it wrought, The Coalesced were born as sentient piles of sludge. Over time they have developed forms more humanoid in nature, but they yet harbor fears of being rejected by other cultures for their close connection to The Doom.
I hope y'all like The Coalesced! I was already toying with an extra ancestry, but the realization that Doomspawn doesn't need to be its own ancestry anymore just gave me an excuse to put some slimy folk in Gaia. Thanks for dropping by! If you have any questions or ideas feel free to rebug them and I'll interact!