Greenman vs. Foksaurus (グリーンマン対フォックザウス, Gurīnman tai Fokkuzausu?) is the twentieth episode of Go! Greenman.
Tonchiki, eager to impress his master, briefs Maoh on his latest scheme which this time requires the aid of Foksaurus. Maoh approves of the plan despite Tonchiki's record of failures. Not too far away, a young boy is seen trying to fish a doll out of a small body of water with a stick. But, he accidentally knocks the precious plaything farther into the water, bringing tears to the eyes of its owner, presumably his sister. Though, there is no time for weeping as proven by the doll's spontaneous combustion and the appearance of Foksaurus! The children dash away as Foksaurus trudges closer and manage to signal Greenman. Arriving in the nick of time, Greenman safely escorts the terrified youths as he attacks the foe in a blinding frenzy of punches. Beating the devilish fiend to the ground, Greenman's success nears ever closer. The hero shows no signs of easing, further infuriating Maoh. But the battle is not over yet; Foksaurus disappears into a fountain of smoke, and reveals his gargantuan form. Stunned, Greenman calls forth his electronics to alter his size as well. The giants of good and evil converge in a small town, determined to destroy one another. However, Greenman does not forget his morals, putting the battle on pause to throw an Ear Boomerang at the tormentful Tonchiki. Losing interest in the children he was chasing, the devious hellspawn orders Foksaurus with his universal command "Chi Chi Pui Pui No Pa!" It soon becomes apparent what exactly this instruction consists of, as Foksaurus begins to emit a yellowish breath. Greenman attempts to combat the substance with another Ear Boomerang, however it is instantly destroyed, causing a powerful explosion which ignites the lingering toxin. In a horrible turn of events, part of the city is engulfed in flames and acts as a fiery imprisonment for Greenman. And to make matters worse, Foksaurus deliberately adds more fuel to the fire, generating even more unbreathable smoke. The perilled savior, gives it his last effort to retaliate, firing off a single Leg Arrow which barely even reaches its target. But just when it seems all hope has been lost, Greenman confidently stands and puts out the surrounding fire with the Fire Fighting technique before dropping to his knees, drained of power. Albeit, he proudly rises once more after much provoking, and fires a successful Leg Arrow before charging forth in combat. Strategic maneuvering and strong blows drive Foksaurus to dart away with fright. With Greenman close behind, Foksaurus gives it everything he's got, pushing out the last of his flammable breath while Greenman simultaneously fires Breaster missiles concluding the dramatic confrontation with a bang.