What a tough guy haha. Very cute.
I'm curious though, as to if this behavior will continue or if he'll start humping it, as he is already mounting/pinning it. Phoebe has a moose toy she was "raised" with who she used to attack and now she loves to hump it... Although her way doesn't look like dominance... Enough of my weird rant.
Your pup is really adorable though!