Sent to Earth by the war-like alien race known as the Megans, the Mega-Monsters - Rhiahn, Triax and Krollar - were sent to slay the most powerful creature on the planet, the only one strong enough to stand in the Megans' way: Godzilla.

Krollar arrived on Earth with Rhiahn, just a few moments behind Triax. They quickly joined the fight - Triax and Krollar tag-teaming Godzilla, Rhiahn attacking Red Ronin. Despite their superior numbers, Godzilla was able to hold his own against the two of them. With their warship crippled, the Megans gave a last-ditch effort and zapped their Mega-Monsters with an Energex-Ray, doubling their size and making them all tower over Godzilla.

With Red Ronin gone and their power increased, the Mega-Monsters attacked Godzilla with all their might. But even with their enhanced strength, the three of them were no match for Godzilla's rage. Godzilla grabbed ahold of Krollar, who tried to escape underground. The giant insect attempted to attack Godzilla, but the King of the Monsters scorched it with his atomic fires, then crushed it with his foot.

As its Megan commanders screamed in frustration, Krollar was slain.