Aarch and Artegor's fight in Friends and Enemies. It's supposed to look serious, but the animation is so awful that it looks hilarious.
Pretty much any of the Snow Kids attempts to play goalkeeper in The Suspension with special mention to D'Jok for hitting his head and Tia for barely missing the ball when it shot practically right at her.
Another that's not In-Universe for that episode being the fact that Micro-Ice performed quite well in his attempt at goalkeeping. It is damn near impossible to block so many footballs being thrown at you at the same time.
"I have to like her, she's my cousin!"
I don't know if this is for anyone else or just me but I can't get serious at anything about Sinedd because of his voice. He sounds like he's in the mix of puberty. It was fine in the first season but for two and three it's both distracting and hilarious.