Battlezoo Ancestries: Fusions (5e)

From the introduction:

Whether they’re a human, a dragon, or even the avatar of a dungeon, species are made up of individuals, with each member of that species being a single distinct creature… or at least, that should be the case. However, some heritages composed of multiple individuals in a single body baffle even the most sage of philosophers as to the physical and metaphysical implications. While these heritages are different enough that some mainstream scholars consider them to be wholly unrelated, scholars have recently classified these gestalt entities into a single speculative species, which they’ve called “fusions.”