Speculative mmo race #2. I guess these and the Cervine would be from some Guild Wars-esque sword and sorcery fantasy.

Kerberos

-Can’t equip helmet items, but have a special collar items
-Heads grow in with age, born with two, and the average Kerboros can grow up to five.
-In mythology legendary Kerboros heroes are depicted with 6 heads. Gods can have over 100.
-Heads have slightly differing personalities. Kerberos whose heads all have the same personality are seen as charismatic (unsettling for non-kerberos races), and usually wind up in leadership roles.
-Think out loud, arguing between heads.
-Mental illness manifests as heads with vastly differing and antagonist personalities that attack each other. Having only one head or heads that are very slow to grow in is a sign of developmental disability.
-Can be male, female, both, or neither. Outwardly no sexual dimorphism.
-Have weirdly malleable DNA. Can breed with most other races, and offspring (always Kerberos) will pick up traits from their father species. Also much more easily affected by radiation, and toxins, and have an extremely high rate of cancer.