Well it doesn't have to be a fruit. Chimera exist even in us humans but mostly in animals that gives birth to many offsprings in one birthing. It's when two fertilized eggs fuse together to form one. Every part of that body will use different DNA blueprints. Like the heart can use egg A's DNA while the lungs take egg B's DNA. There will not be two people in the same body so split personality wont appear.

That is also why this is the strongest candidate for BB's condition. And the way they speak about him also sounds like it's Blackbeard's own body that is different and not a fruit. Also there is nothing about the Greek mythology beast Chimera that indicates that he should be able to absorb anything. And even if it's based on that he should be able to absorb 1 more (3 total). The Chimera fruit in itself should not count as one as that is the base and the 3 entity's should be able to absorb one each.

But if he can absorb one more, IMO he should go for Marco's. That generation is an awesome ability in itself and it would also offset any damage he would "draw in" from his darkness fruit. Also give him the ability to fly and almost logia-like properties. That way he would have one of each type too. But talk about broken. Who could beat that without using seastone?