1. I've never seen Epona in the wild. I assume it's amiibo-only, but if it isn't, I assume she's hard to find. 

2. It can, and it's even needed for a side quest. You just need a butt load of stamina or stamina-restoring items. I think I used three whole stamina wheels before it calmed down (2 standard plus one restored with a potion).

Just spam the L-button (or whatever the Switch's equivalent is) to calm that one down, easy peasy.

Since we're on the subject of Horse photobombs.

oh that explains a lot i only did one stamina upgrade. Guess I will go tackle him after getting more upgrades

Horses are so majestic that sometimes they're annoying. It's like learning how real horses act and I'm not very good at that.

First thing I noticed with the horse was how touchy it was with anything, slight slope, enemies, little steps... I thought horses were going to steer away from sudden halts (similar to the MK8D driving assist), veering away from obstacles, etc. Miyamoto mentioned that in 2014, and it sounded natural that the horse would try to avoid things. It certainly doesn't happen when you gallop, but when stridding the horse does follow the path.

Sucks to be you, I guess haha.

I'm glad someone agrees with me! That game is truly a masterpiece on so many levels. One of the few games that actually made me contemplate and reflect on the impact the story had on me when I finished the game. If that game looked like Horizon I would die a happy man! But man, the game has aged rather well anyway. :)