Meet Buster, the SUBSTITUTE teacher for  PokeCombatAcademy.

What classes does he do SUBSTITUTE for? All of them. Mostly Phys Ed., of course, as Buster is well trained in the art of being a SUBSTITUTE dummy. He's also surprisingly effective at keeping watch on students during Detention, though most students woudn't be able to explain just why that is.

Buster is a mystery. He (most assume is a he) is said to have been part of the school since its very beginnings. No one knows what his true form is, or if he ever even had one, though the more popular rumor is that he belonged to a Keckleon or Cubone teacher who fell ill during a class, used his SUBSTITUTE to keep tabs on his students while he was hospitalized...and never returned to the school again. Most faculty members will merely claim that rumor to be pure nonsense...and hide well the fact that they don't know the answer to this themselves.
Others claim Buster is actually a Ghost-type who took possession of the doll for reasons unknown and is now unable to free himself from his "host". This rumor is also enforced by the fact that Buster has an uncanny ability to show up whenever the need for a SUBSTITUTE teacher is there.

But to the grand majority of the school, though, Buster simply is. As he has been, as he will always be.

---

Slap me repeatedly for this idea, please.

BTW, guess why I named him Buster, win a cookie.