Big Macintosh is both strong and big, but nopony can keep on top of that kind of pile forever. As he sinks, the doll gets closer and closer to the other ponies.

Finally the mayor, of all ponies, manages to get high enough. "Give me!" she shrieks, and snatches it. Then she tries to run off.

A few of the piled ponies have realized that Big Macintosh no longer has the doll. Between that and the sudden need, not just to keep it, but to get it back, he manages a burst of strength that sends them flying. "Nnnope," he says, and charges after the mayor.