My theory right now is that Tizzy isn’t actually Tizzy.
Tizzy has been around for almost forever, and has presumably been annoying people for at least that long. My thought is that the Concordenax got fed up with him and killed him and tried to devour his soul. Tizzy then somehow possessed him. When the concept of devouring souls came up, Tom was told that the victim can sometimes fight back and even take over, or worse. So Tizzy is almost two full demons, which could explain his appearance, insanity, use of powers he claims not to have, and the many historical instances of someone named Tisdale ( or a derivative) saving the day, among other things. The demon weed could help his multiple personality issues.
I didn’t explain it very well, but it seems reasonable to me.