Big Serow is White Leo's adjutant, a fierce but fair fighter and tactical specialist in the war against the Decepticon conquerors on planet Beest. He is the King of Saitan, the country (one of 38 on planet Beest) of his birth. Presumably this was his occupation before Alligatoron's Decepticon-backed uprising sent White Leo's followers into hiding. He is specifically targeted by the evil Killer Fish for retribution over an injury Serow gave him years ago.
- English name: Deer Stalker
- Voice actor: Yoshitada Ōtsuka
- Big Serow (Beastformer, 1987)
- Beast ID number: 2
- Accessories: "Big Boomerang" blade
- Big Serow is an anthropomorphic serow deer with green robotic armor. His left arm ends in a (non-spinning) drill. He came with his "Big Boomerang" blade-weapon. His rubsign reveals one of three symbols; Fire, Water or Wood.
- Big Serow white version (Beastformer, 1987)
- A solid-white version of Big Serow was sold through gumball machines in Japan. The gumball versions of the Beastformers appeared to have randomized weapons (or just crummy QC).
- "Big Serow" seems to be a misnomer, as serows (a species of ungulate found in Asia) tend to be more goat-like, with bushier coats and short horns.