You don't really fight in Poptropica. You just solve mysteries and such
You can "fight" a sumo wrestler in Red Dragon island and on the free mini game inspired by the island.
No you can only play games with people.
run
you fight the monster under the hub
you fight bad hairless man
to make you look cool.
buy prepare for impact in the store
you fight Zeus to become a god
you fight the robot on jungle planet
shoot it or run away if you have at least 1 cannon
You get hades crown and posidens trident.
you go to Mount Olympus and fight Zeus