The A.I. is actually very simple, the horse moves forward when you get too close and jumps if it hits the side of a block.
Yes, I knew that it moves when you get close, but I didn't know how how did you make the jumping. I would probably create an empty GameObject with a collider set to trigger, put it on the right side of the horse and set that GameObject as a child of the horse, so that it would move with it. Than I would create an OnTriggerEnter2D void in a script attatched to that empty GameObject, which would detect wether it touches anything with a certain tag (All the groud GameObjects would have that tag) and if it does, it jumpes. Did you do it the same way?