S1·E17 Battleground

Ming's forces travel to the planet Grubor, where they use his freeze-ray weapon to capture six Cave Slugs- invincible alien creatures the size of semi-trucks who can and do eat anything, including rock, metal and laser beams. They are harmless unless provoked, whereupon they counterattack with tremendous force. The Merciless One deploys his first Cave Slug in a mine tunnel beneath Monitor, and as the alien munches its way towards the Defenders headquarters, Kshin and Zuffy stumble upon it and must be rescued by the Defenders. At the time the Cave Slug breaks through the top of the Volcano and heads to Central City, Ming places the five other Cave Slugs in major cities all over the world. The Defenders make the costly mistake of attacking the Cave Slug, sending it on a rampage until Jedda uses her animal telepathic contact abilities to make peace with the alien monster. Infuriated, Ming decides that if our heroes won't provoke the creatures, he will; however, his attack on the earth is crushed when the Cave Slugs counterattack Ming's forces. The misunderstanding settled, the Defenders happily transport the Cave Slugs back to Grubor.