So I was walking through the woods one day, and I thought to myself. Hmm, maybe I should beat the Broodmother. So I tamed up some Rexes and I took off onward to the green tower. So I traveled until I got to this tiny little ledge to get to the middle of the tower. So I ran up and whistled for my army.
...every single Rex fell off
P.S. I Teleported to the Broodmothers arena 30 min later.