Welcome over to the crafty forums!
I've been mulling over that Oni Mask build a bit since you posted it on the OOC chat from our myth-weavers game. Have you considered treating the "mask in charge of a man" build as maybe doable by simply giving a human/elf/pech/whatever (the person you're on top of) the Ogre blooded and Fire brave feats to represent the effects of the mask? If you aren't planning for the mask to remove itself except in very special circumstances, the floating part can maybe be fluffed somehow. And the capacity for the mask to remove itself and reattach to a new dupe if the person it's on is killed could maybe be covered with the cheating death rules somehow.
I had wondered about brewing a cyborg feat, incidentally (granting a few of the unborn immunities, or equivalent resistances, and access to the fun that is unborn species feats), but I haven't got around to it just yet.
On Build 2, may I (somewhat self-servingly) recommend a Monster speciality I homebrewed
? It seems appropriate (even if the formatting etc. went a bit wrong when I posted it to the database).