Jackson's theme should more like a mix of the Kaos fight from Skylanders trap team and with the Giga Chad Epic theme
Kaos theme: https://youtu.be/I6HUHfC7usE
Giga Chad's theme: https://youtu.be/_7cOLeI3EgQ
knifeboi's battle theme should start off with a simple 8 bit melody and then after a few seconds quickly build up into something epic as he activates his neo form (rather like megalovania). Also if you're using fl studio I recommend getting plugins like NES sounds and earthbound sounds because you can make some epic tunes with them.
Beldum: something like an orchestral thing with trumpets and everything as well as choir
Zanthor: a rock kind of music with an accordion and violin in there
Inkmatas, can you make her theme similar to Supreme Calamitas' theme from calamity mod (Stained, brutal calamity)
Stained, brutal calamity: https://youtu.be/MT6HTpY_OyE