so in the quest to ride cool creatures I came across this possibility but I'm just throwing it out there to see if anyone has tried it before or thinks it's doomed to fail from the get go.
Nature Oracle gets a bonded mount which is classed as a full Animal Companion including share spells
Spirit Guide gets you wizard spells of the same level on your spell list looking at you form of the dragon I II and III. Kicks off at 12th level , unless small rideable at 14th level.
Your a bit limited with your mounted combat options being stuck in the Nature mystery. And spirit guide needs Cha so have to dump stat elsewhere.
And of course the spells don't last that long but they'll work long enough for some fun.
Of course having access to all the wizard poly spells you could make your horse just about anything anytime you want to, not to mention some of the best frontline buffs you can get.
Heh you could have a dog mount grab the blink spell and make a blink dog, though your GM might just make you roll to see if you fall on your ass while riding it ;)