Having seen his handiwork throughout the NLCS, I'm pretty sure the Cardinals could replace Mike Matheny with one of those horses who picks football games by tapping the picture of the team, and it would constitute an improvement.
'OK Manager Buttercup (or Royal King, or whatever you name horses), we've laid out pictures of all the players. Now who bats leadoff?'
*horse taps Matt Carpenter's picture*
'Great! What position will he play today?'
*horse taps ground 5 times*
'3rd base, good call.'
Also, a manager might finally win an argument with an umpire. Imagine being an ump and a freaking horse comes charging out of the dugout to dispute your call. You gonna toss a hose from a game? I don't think so. Those things have big teeth. Also, they can stomp on you. Not sure what kind of suspension MLB would levy for stomping an ump to death, but as long as the horse is wearing MLB-approved gear, I'm sure it won't be too bad.
Mostly, I'm pretty sure the horse won't decide that in the 9th inning of a tie game the team has to win to stay alive, that it's a good idea to use a pitcher who hasn't pitched in three weeks. I can't even fathom the train of thought that made that seem like a sound decision, outside of "Man, I really want to start my winter vacation."
Of course, there could be some clubhouse communication problems, and they'd have to replace the dugout steps with a nice ramp so Manager Horse could enter and exit safely. Don't need a manager with a broken leg. But those are minor details, and the horse might enjoy it. I'm sure all the players would try to feed it apples and carrots in exchange for more playing time, and the team would be able to market all sorts of new merchandise for horsey-loving young girls and boys who would adopt them as their favorite team.
Yup, I really don't see any possible flaws in this plan.