I have a couple of fun characters I'd like to try out sometime but I'm having trouble building them. Any advice would be appreciated, I prefer someone that's fun to play over strong, but they shouldn't be a drain on the party either.
1st: Zoey the Chaos Mage from Orcs Must Die
About Zoey, she is a straight up Wizard, with a bat familiar, what makes her unique is that she cannot control her magic. In Orc's Must Die, she had the highest damage potential of any character however her magic randomly changed schools. You would never know if she would attack with fire or electric or anything else. I like the idea of an RNGesus spell caster who's evocations (or other spells) are slightly stronger but at the cost of control. I just haven't seen anything that could build this well.
2nd: a Centaur
I personally allow point buy based on race type, so I allow Kobolds at 25 point buy and Centaurs at 5. I would like to make a Centaur that is the mount for another PC, and I'm wondering what 2 builds would mesh together. The rider's build would be odd for a mounted build because you don't need a mount from the class which most mounted builds provide. My first thought was both Barbarian's raging together, but that doesn't make a good team as you have 2 PC's playing the same role.
There's a couple of mounted archetypes which don't get mounts, notably sohei monk. It'd mesh with anything really, but there's a cavalier archetype for centaurs called the charger, and with the right order the charger could buff the rider in turn. On the other hand that's two melee grunts which won't want to be separated, much like the 2 barbs problem you mentioned they don't especially fill any other party roles. Maybe two more general buffers would work better - bard and cleric perhaps.
A spellscar mystery oracle is all about the primal (wild) magic as is a primal warden shaman. There's a primalist wizard archetype which uses it a bit, and arcanists can pick up exploits related to primal magic.
For a character that is to be a Mount, I would totally go with a Druidzilla Build. The way I like to do it is to take 4 levels in Druid, and then at least 5 levels in Warpriest, applying Sacred Weapon Damage to your Natural Attacks which then scale up 2 sizes by the time you are a level 8 character: take Shaping Focus, and your nondruid levels count as Druid levels for the purposes of Wildshape, maximum level 8, which is enough for you to be 24-7 in Animal form, and you can turn into up to size Huge Animals. I have 1 or 2 tricks in mind to make the Full Attack even scarier.
Primal Warden Shaman looks like a pretty good match for a Chaos Mage
Wildshape isn't useful if I'm already a Centaur and therefore can be the mount without wildshape. Warpriest is a good idea though, buff the natural attacks and get some spells/healing for utility and fill a role other than combat only.