You are a player on a Mount that is your Animal Companion.
You command your animal companion, giving it 2 actions. The mount uses one of it's two actions to Tumble through an enemy... while you are mounted. Mount makes an acrobatics role vs enemies Reflex...
And that's it? You, the rider / the player don't have to make any checks?
That's how I see the rules as written, coming here to get some perspective.