My first reaction to this card was "Oh great. Another AleP card that's over-powered." I originally compared Bob to Westfold Horse-breeder, because of their similar ability. For only 1 more resource, Bob has you search your whole deck, immediately dragging out ANY mount or pony card you want. I mean, that is on the same level of scrying as Word of Command or Gather Information, and the requirements to make those work are steeper (i.e. you have to exhaust an Istari character, or spend a round passing a side quest). Granted, Bob only fetches you a mount or pony card, but if you are playing a Gandalf deck or maybe need a Rohan mount card, he gets it for you--a little too easily.
On further consideration, I think I judged a little too harshly. One thing that limits Bob is that he is unique. You can play multiple Westfold Horse-breeder to fetch you army of horses, but you cannot have multiple Bobs (I swear I'm not trying to make a Raising Canes pun lol). Yeah, you could sneak attack him, or kill him off, but that seems like a lot of work. I think Bob is a powerful ally indeed, but A: he is , so he doesn't really have a place in my Rohan decks, and B: he is limited to (probably) once per game. One good synergy he has is in a hobbit deck, grabbing Bill the Pony to boost some hobbit HP. I do not think he is OP, and I think the designers did a good job on him, thematically as well as practically. Not loving the artwork (Why does he have elf ears???) but that's OK.