Art by Keith Page
Green slime (or green sludge) is a chemical compund created by Colonel Brown and his assistant in the Marko's Magic Football series. Brown planned on taking over the world with the slime, turning Planet Earth into a "polluted, yucky glob". It is capable of turning living creatures into monsters and turned Marko's regular football into a magic football.
Barrels of the sludge can be found all over North Sterlington. Marko first encountered one outside the Toy Tower. The child accidentally kicked his ball into a barrel of slime and believed his toy to be ruined. However, it quickly returned to trip him up and he soon realised he had a magic football. Later, as Marko was dreaming of this, he was confronted by a police officer, but his pursuer failed to see a barrel of slime and crashed into it, spilling its contents all over him. Before long, the sludge changed him into a monster who attacked Marko by firing slime projectiles. The officer half-changed back into a human and retreated into the sewers.
Marko followed the officer-monster underground where he narrowly dodged slime leaking from the pipes. Things got worse when he was confronted by three slime-covered "dinosaurs", but he easily defeated them. Soon, Captain Smirk arrived from the future to warn Marko of the slime's properties and Brown's plans. Back on the surface, Marko found himself engaging in battle with a clown capable of shooting slime from his lapel flower.
In the Toy Tower, Marko was about to destroy a chemistry set developing the green sludge was stopped by a pair of welders "brainwashed" by the sludge. Brown ordered Marko into a barrel of sludge but Marko escaped and a loose shot from a welder's flamethrower caused the slime fill the room. The Colonel then tried to attack Marko with a custom-built sludge gun but was kicked into the slime wave by Marko's football. A reaction with Brown's special suit caused the slime to explode and destroyed the tower.
At the end of the story, green slime was seen trickling in or out of a drain, suggesting that problems still lay in the sewers.