Giant kangaroos

The giant kangaroos were huge siege kangaroos that Momon used to attack Wipe Castle in Cornwood. Their joeys are the size of regular kangaroos. Some of Momon's soldiers rode in their pouches during the attack on Wipe Castle and threw spears, unicorns and the kangaroos joeys at the castle. The Great Wizard Greyfarn tried to use a giant boomerang to kill them, but it came back and knocked him down. They had a powerful kick that could after several kicks, tear down the walls of Wipe Castle. They were likely killed by the centaurs' arrows.

Trivia

 * In "The Birdbot of Ice-Catraz", Bender Tells Fry a story about saving the children of Australia from a giant kangaroo, though it is most likely not true.
 * They are based on the oliphaunts (giant elephants) from Lord of the Rings and even have similar face paint.