I've been looking up strategies on how to beat him, none help. I'm not sure how to buff/debuff him, my characters as far as I'm aware can't do saboteur or synergist, I'm trying to figure out how to keep his health from regenerating... can I buy poison from the woman dressed as a chocobo? My characters can paradigm shift with ravager, commando, sentinel, medic in many different orders of those 4... what's the best strategy?
ITs been too long since i played to remember a stratedgy so I can't help there, but i will say this: I beat the game w/o ever using syn or sab even once. That was prob not the best way to go about it, but i went through the game with just the four classes you mentioned, so dont give up hope its not impossible.
I spent about half an hour trying to come up for a strategy to beat him, but to no avail. Your just going to have to level up and have a dedicated sentinel if you need to, make sure you have a sab for his buffs, and you'll beat him easily.
You seem like you've came into this game not playong XIII... Anyways I'll make this quick and simple...
A SAB role debuffs your enemies (gives them status aliments like poison, deprotect, deshell...) and a SYN role buffs your party (gives them protect, shell, veil...)
To counter Caius's rapid health regen, land 'Poison' on Cauis, you will have to do this a few times as he gets rid of all his status aliments and his chain gauge a few times... The best person to give the SAB role to is Serah, and Noel's the best person for the SYN role.
Also, I hope this playthrough helps you with the Cauis fight, Olizandri is a easy proven gamer, who, always shows his techniques in the simplest way.