Ok, so the episode this happened in was episode 4 - season 2 of Alien Force, titled "Save The Last Dance" aka the mpreg episode.
The episode opens up with some teens driving an out of control car. (The breaks weren't working. Why is never explained).
After Ben saves them as Big Chill they try and thank him, only for Big Chill to suddenly get the munchies and start eating the roof of their car.
The two guys are understandably annoyed and call him out on this but Big Chill just sort of hisses at them menacingly -Cue Opening Credits- (these two guys are never seen again, which lead to a friend of mine making jokes that Ben ate them for a few weeks after this episode aired).
Side Note: Something my friends and I used to joke about was how in many episodes of UAF, the writing unintenionally lends to the idea that Kevin and Ben are into each other as Kevin frequently favors Ben over Gwen, his actual love interest, many times throughout the two shows. It's to the point that my friend think it's entirely plausible that Ben and Kevin are seeing each other behind Gwen and Julie's backs and he can not be convinced otherwise.
For example, once the opening is done we cut to Kevin's house. He's working on his car and Ben... is in the garage bathroom brushing his teeth and using mouthwash. Did Ben stay the night? Did something else happen?
As Ben is cleaning his mouth out he discovers a metal shard in his teeth.
How on earth he failed to notice it until that moment is beyond me.
Gwen comes in and rather forcibly asks Kevin out to her school dance, which freaks Kevin out because he's gay she goes to a prep school and her school dances apparently involve sit down dinners, and he might have to waltz, and he knows nothing about the different types of forks (he even calls them "finger fork").
He ends up going to Ben for advice. This scene is actually very cute because Ben is very sweet about reassuring Kevin and I'd share it if I could find the clip. Unfortunately for Ben, Kevin is too concerned with preparing for the dance via watching videos on waltzing and forks. (Kevin is my v dumb son and I love him).
With no one else to go to Ben turns to Julie, recruiting her the follow him around on her moped and writes down what he does when he's in his alien forms to figure out what's happening. Ben initially tries to turn into Jetray, and he does... only for the Omnitrix to override the command and turn him into Big Chill a second later. He proceeds to reek havoc by eating a bunch of metal around town.
Ben wakes up next to giant hole in what appears to be the desert that apparently surrounds Bellwood in the UAF seasons.
Immediately after this we get the second most infamous scene in this episode. The "Ben eats a whole jar of pickles while helping Kevin dress up" scene.
After this Julie meets up with Gwen and voices her concerns. Gwen doesn't think much of it and talks about how she's worried Kevin won't go to the dance with her. Ben shows up and Gwen leaves to give them some space. As Julie fills Ben in on what happened the night before and assures him she's going to do what she can to help, Ben spaces out, and turns into Big Chill again. She tracks him down to some kind of steel beam plant??? Anyway, he gets in a fight with some security officers.
He then drinks molten metal before flying off. Julie tries to give chase but he freezes her moped a bit, which puts her out of commission long enough to return to THE HOLE.
Where he regurgitates the molten metal.
As Kevin drives himself and Gwen to her school dance, he recounts how Ben gave him helpful advice. This causes Gwen to remember how Julie was worried about Ben before and she realizes something might actually be long. Literal seconds after telling Kevin this, Julie calls and informs them that Big Chill is going on a rampage.
Using Kevin's Plumber Badge they're able to figure out where Big Chill is and decide to meet up there.
As they drive, Gwen recounts how one of Ben's previous aliens, Ghostfreak, went rogue, and comes to the understandable conclusion that Big Chill, another ghost-like alien, is doing the same. (Spoiler: That ISN'T what's happening).
They arrive and find Big Chill standing on some kind of metal... thing. Kevin and Gwen understably assume that it's some kind of doomsday device. Julie and Gwen try to reason with him, but Big Chill isn't having any of it. Kevin decides to do what he does best - PUNCH. This leads to a fight that eventually results in Big Chill getting knocked out for a few moments.
Gwen comes to the conclusion that the metal thing is causing Ben to act the way he is, leading Kevin to try punching it. This ends badly for Kevin, as green goo squirts out and ruins his tux.
Then we get the most infamous scene of the episode.
The episode ends on Kevin and Gwen dancing to his car radio in Ben's now empty nest because because they missed prom.
And that's how Ben Tennyson became the teenaged parent of 14 cyrokinetic ghostly mothman alien babies at the age of 15.
And before you ask, no, the events of this episode were never brought up again. Although it has since become a common topic of fanfics.
As you can imagine, the entire Ben 10 fandom was basically the below image when episode aired.
gummygunk
areudirty
s-u-f-j-a-n-s-t-e-v-e-n-s
kianamaiart
discoholicmusic
germansingergirl
