Greenman vs. Antguirus (グリーンマン対アントギラス, Gurīnman tai Antogirasu?) is the second episode of Go! Greenman.
After his previous monster failed him, Tonchiki plants a second monster, Antguirus into a colony of ants. After one of the children stomps on the ants, they combine into a large ant that latches on to the child's leg. The remaining three children use the Green Calls to summon Greenman, who pulls the ant off and tosses it off to the side. Fearing defeat, Tonchiki further mutates the ant into Antguirus. Greenman first tries to throw one of his Ear Boomerangs at the monster, but it proves ineffective. They then charge towards each other and begin to fight. Nearing closer to the Underworld's entrance with each punch, Antguirus eventually beats Greenman to the ground and drags him in to the lair. Now inside the Underworld, Antguirus further beats on Greenman until he eventually bites the hero's arm and injects a black liquid into him. Seeing that their hero is near defeat, the children use their Green Calls once more to strengthen Greenman and rid his body of the liquid. Antguirus continues to fight until he is beaten to the ground, allowing Greenman to fly back to the surface. But, Antguirus follows him out; so, Greenman grows to giant size in order to defeat him once and for all. Antguirus does the same, and they continue their fighting on a small mountain. Attempting to put up a final fight, Antguirus sprays the black liquid towards Greenman, but it misses and instead burns Tonchiki who is watching from the ground. Greenman eventually beats Antguirus to the ground with the Greenman Stick and finally destroys him with the Breaster attack.