The MBC is shocked when Mr Smith's sister, Aunt Frida, comes back to visit them, except this time she informs them that...she's married! And her husband is a famous opera singer! But things are not what they seem, and Moochie is certainly full of surprises! In the meantime, Sam gets stuck with Aunt Frida who is working on a secret recipe.
King Petalia comes back to ask for the MBC's help, as he's being pursued by the evil clipper-bots again. Soon, they realize that they've been sent on a wild goose chase and it turns out that King Petalia is not nice anymore! He came back to earth to abduct Jeremy, hoping to steal some valuable information from him.
Gilbert is back to Singletown! Having learned his lessons from the previous time he was in town, he comes bringing a "Thank You" gift for the MBC, but unfortunately things go a little out of control! The MBC have now to face a laughter epidemic !! At the same time, Mark needs to get a computer from Jeremy and finds himself wooing Cathy so he can be her girlfriend!
Random objects begin to disappear around Singletown, and some objects end up in the weirdest locations! The MBC investigates and soon discover it's the work of an very tidy alien who's only goal seems to clean up Singletown. All of Singletown is threatened to be turned into a spotless town, humans included!
An exciting event takes place in Singletown: a solar eclipse! Soon, this exciting even turns out to be more than just exciting: completely weird! The eclipse doesn't end and Singletown become the target of an alien who wants to turn it into a giant night club! At the same moment, Cathy gets assigned a new mission from the commander that she has to succeed if she wants to keep her club membership!
While Cathy and Chris battle the ever-increasing Annihilator forces in the present, Danny and Sam are in the past trying to alter the course of the future and prevent Mark from ever getting his hands on the tape. However, their efforts keep failing and, back in the present, the Annihilator mother ship has arrived with its Death-Star-style beam to flatten the town.
Mr. Smith puts the MBC in charge of protecting a small black orb. What they don't know is that the orb actually contains an entire galaxy! And things get really tricky when a vicious spider alien confuses the orb with her missing egg! Meanwhile, Mark challenges Danny to a bowling competition on his own private bowling lane.
Mr. Smith surprises the MBC with a special performance by a great magician - Rhubarb the Remarkable! However, the gang is shocked to learn that Rhubarb is actually a "reformed" bad guy that they defeated in episode 10 - Wedge, the talent agent. They're suspicious of Wedge right from the start... and with good reason.
Glutin the Sticky alien returns to Singletown Middle School and he's out to bag himself a Rhapsodian. The MBC immediately assumes he's after Cathy, but they're mistaken. You see, during a mishap in Fuster's class Cathy's powers have inadvertently been transferred to Wendy! The MBC has to try and reverse the effects before Wendy gets out of the school... or gets captured by Glutin!
When the MBC breaks the record for "monsters busted in one month" they receive a reward from the IGA commander - flying lessons on the ultra-cool V-9 spacecraft. But, as it turns out, the flying lessons are all a ruse. It's a plot by their old friend Herptilius to kidnap the MBC and ship them off to an intergalactic barbecue... where they will be the main course!
When Jeremy accidentally comes in contact with an alien substance, he undergoes a strange transformation - turning into a hideous monster whenever he sees anything Rhapsodian. The MBC must figure out how to reverse the effects before Jeremy destroys everything. Meanwhile, Sam gets blamed for injuring Mark and Rollins forces her to assist Mark with his hideous science project.
When Singletown goes into an unexpected deep freeze, the MBC suspects alien activity. It turns out that Pizmo, a reformed eater alien, has turned the town into his own personal workout facility. He's created a cooling machine so that he won't sweat during his insane workouts. But now the cooling machine is out of control and threatens to throw Singletown into another ice age.
The MBC unearths a time capsule left behind by the original MBC, warning of an attack that is due to take place in the future. The MBC receives a series of encrypted clues, which they must follow in order to avert certain disaster - in the form of all the aliens being released from the containment grid! Meanwhile, Mr. Smith's sister Frida shows up for an unexpected visit.
When Singletown experiences some strange weather patterns, the MBC discovers that the entire town is covered with an alien Jellynerp. The creature was placed there by the local weatherman - actually an alien - who is tired of reporting the weather and wants it to be the same every day. A sound plan, except for one minor detail: now the Jellynerp is hungry and it's starting to eat the town!
The MBC investigates a strange caveman-like alien that has come to earth and is reaking havoc around the school. Krog's destruction seems to be random, until they discover what he's really after - the hand of Principal Rollins! Meanwhile, when the MBC decides that Sam needs to "lighten up" a bit, Cathy takes it upon herself to try some strange Rhapsodian techniques.
A group of bubblegum-like aliens come to earth to seek refuge from their planet (Bagumblia) which is suffering from global cooling. Their leader is angered when Danny inadvertently chews him and declares war on humanity, taking Mark as their hostage. The Baglumbians threaten to unleash their hideous mastication monster on Mark, and the MBC must leap into action to protect him.
When Danny and Sam mess up a few assignments, the IGA commander sends down two droids to assist the MBC. But, while Chris and Cathy get along with the new recruits, Danny and Sam suspect that they're up to no good. Meanwhile, Mr. Smith recruits the MBC to help him plan Cathy's "Sweet 250" birthday party.
Little John inadvertently subjects the MBC to the effects of his truth ray, causing them to suffer strange physical effects whenever they lie. This complicates their efforts to subdue an intergalactic villain. Meanwhile, Danny gets an opportunity to work with Wendy on an assignment - "Life on Other Planets: Fact or Fiction." But his inability to lie causes big problems for him as well.