Futurama

Luck of the Fryrish I believe.

That or the movie where he loses his lucky pants

Either way, he declares that his luck is changing right before the ladder he's climbing into the sewer has a bar break off, sending him plunging into either just the water or onto someone slimy

Edit: wait, it's definitely Luck of the Fryrish. They're heading to Old New York to find Fry's clover. Same deal, the ladder breaks after he declares no more bad luck

In which the mutant underground is first established?

Luck of the Fryish, I think, right after Fry declares his bad luck is over and then slips and falls into the sewer.

Pretty sure that’s from “I Second that Emotion”.

Bender flushes Nibbler down the toilet, but the Professor fits him with a chip that makes him feel Leela’s emotions. So they head to the sewers to find Nibbler.

"Ugh... and the aftertaste"

I think the one with the 7 leaf clover?

El Chupanibre episode??

Hard? Looks like I'll need a little luck!

uh, my brain is thinking the one about Slurms MacKenzie, I think there was a sewer in that one?

EDIT: https://en.wikipedia.org/wiki/Fry_and_the_Slurm_Factory

He was fun!

Google reverse image search says "The Luck of the Fryish"