Mutant head

Mutant Heads were a gimmick present on the the majority of early Beast Wars toys. A portion of these toys had two heads, one of which was a biological-looking "mutant" head and one of which was the actual robot head of the toy. Other toys utilizing this concept instead had masks which covered the robot face, or heads which could be rotated to show either face. While this concept was never explored in this continuity's fiction, some characters are more identified by their mutant head than their robot head, such as Waspinator or Tarantulas. In cases of redecos of molds with this feature, the new character will often be identified by the opposite head the original character used in the fiction. This is the case with Buzz Saw and Black Arachnia who are both identified using robot heads.

From Teletraan I: The Transformers Wiki, a Wikia wiki.