The Crater Critters are large, brutish rock creatures who bathe in lava and claim to enjoy eating brains. They only appeared once, in the episode Last Action Zero.
The Crater Critters are large rocky-aliens that are shown to wear swimsuits. There are two notable shapes of the Critters. A short, thicker design, who commonly wears swim-trousers, and a tall, thinner design, that are seen wearing bikinis. At the beginning of Last Action Zero, a short Critter is seen wearing a bikini-bottom. The Critters, and their swimsuits come in multiple colors as well. The colors of the Critters themselves are natural colors, such as brown, tan, gray, and white. Their swimsuits on the other hand, come in blue, magenta, blue with yellow stripes, yellow with a pink outline, and yellow with pink flowers.
At the beginning of Last Action Zero, a Crater Critter is seen bathing in a
volcanic crater, remarking that he would enjoy eating the brains of the locals once he is finished relaxing. He mentions that he's glad he beat the seasonal rush, until Jenny and Brad interrupt his vacation, thus prompting him to battle with Jenny. Brad tries to contribute to the fight by tampering with Jenny's Net-o-Matic. This inadvertently hinders Jenny, allowing the Critter to trap the two. The Critter attempts to crack open Brad's skull, but is suddenly zapped by an ice blaster and frozen solid by a 7067 Skyhawk, along with the volcanic crater being frozen as well. The Crater Critter is arrested by the Skyway Patrol and taken to the ship. After Brad is recruited by Skyway Patrol, a spaceship for the aforementioned "seasonal rush" arrives at the volcano. The aliens blame Jenny for freezing the crater and ruining their vacation, and proceed to gang up pile on top of her. Jenny is badly injured, with sparks flying out of her, and dents, but continues to fight the aliens. However, the Critters are able to instantly regenerate their bodies after being harmed. They soon overpower Jenny and attempt to eat her brain, marking how they haven't been getting their daily allowance of iron.
The Skyway Patrol comes to the rescue yet again, but Brad is incapable of helping, due to the all of the excessive paperwork he is forced to fill out before carrying out any task. The Critter that was arrested at the beginning of the episode breaks free in the meantime. Jenny's metallic head is cut open, revealing her robotic brain as the Critters try to eat it, but they are immediately frozen by Brad and Jenny is rescued. Jenny and Brad battle the Critter by shooting paper at it — because rock is weak against paper (according to the Rock-Paper-Scissors game).
The Crater Critters do not make a return in the series afterward.
- "Ah, fresh healing lava! Takes away all the stress of Mercury's hustle and bustle."
- "I'm glad I beat the seasonal rush! After a nice long soak, I'll stroll down to the local village and sample some of the human brains, I've heard so much about!"
- "What the glork?"
- "Gaaaa! No one ruins my vacation!"
- "Spare this, you little party-pooper!"
- "I don't know, after seeing him in action, I'm not sure he'll make much of a meal."
- "Well then... Let's crack your skull open, and have a look-see!"
- "Hey, why's the hot springs all frozen? You!"
- "Pile on!"
- "I guess you could say... That when it comes to... Fighting earthlings... We rock!"
- "Since you ruined our favorite hotspot, it only seems fair that we get to eat your brain!"
- "Oh, good! We haven't been getting our recommended daily allowance of iron!"
- "Huh? It's Skyway Patrol!"
- "They ain't doing nothing."
- "Well then. Where where we!"
- "Oh, goodie! A couple of nice young brains!"
- Despite having deep, raspy voices, a majority of the Crater Critters are actually female. As seen by their swimwear, the female Critters wear full bikini tops over their chests, while the males wear swim trousers or just bikini bottoms.
- Even though the Crater Critters only appeared in one episode, multiple refrences to the Critters, and Last Action Zero have been made throughout the show.
- The short and tall Critters appear to reflect one another.
- The white and light brown Critters both wear yellow and pink.
- Both a short and tall Critter are brown.
- There are two gray Critters that wear blue.
- One of the male Crater Critters wears yellow swim trousers with pink flowers on them, a possible reference to Patrick Star, a character from another Nickelodeon show, SpongeBob SquarePants.
- While not much is known about the Crater Critters’ lives outside of their vacations to Earth, it is likely that they have organized societies much like Cluster Prime, and the Planet of the Bikers.
- The lead male Critter at the beginning of Last Action Zero is the most detailed Critter, (rather than being a simple recolor), likely to differentiate him from the others.
- These differences include: Being the only short male Crater Critter to wear a bikini bottom as a swimsuit, a crack between his eyes, the only Critter to wear purple, and the only one to be shown wearing sunglasses.