Zobie used to be a human boy.
If you've seen the bumper before the Grand Finale, you'll notice that Zobie is a coffin with a skeleton hand poking out of it during the daytime. If he isn't based on a Halloween decoration unlike Kabo, then he is actually based on the ''corpse'' of a dead person. In other words, Zobie Was Once a Man.The Motive for Tubee, Usop and Yumyum's bullying
If you haven't been watching MHS more thurolly, you might've noticed that Tubee, Usop and Yumyum, the latter mostly, usually targets students who either already found their wonders (i.e., Docky) or are trying to figure out their wonders (i.e., Hikky) without no real reason explained. However, in later episodes, it's heavily implied that they're bullying most of the other students is because they're trying to figure out, they're own wonders and they're bullying is probably them trying to hide they're insecurities about it.