A Beagle must use his newly-bestowed superpowers to defend Capitol City from mad scientist Simon Barsinister.

Shoeshine Boy: When I'm bored, I just chase my tail. If you're lucky, you throw up, and BINGO, lunch part two!
Shoeshine Boy: There's no need for fright. Underdog can bite.
Dan Unger: Give him a chance. you might get to like him.
Jack: I don't think so. All he does is eat, sleep, and poop!
Dan Unger: Well then, the two of you have a lot in common.
[from trailer]
Shoeshine Boy: Y'know, you never see dogs hurting each other for money.
Jack: You never see people sniffing each other's butts.
Shoeshine Boy: Touché.
Shoeshine Boy: [starting to speak] Give the dog your food!
Jack: Aaaaaaahhhhh!
Shoeshine Boy: Aaaaaaahhhhh!
Dr. Simon Barsinister: [as Simon Barsinister approaches Shoeshine Boy with a hypodermic needle] Don't worry, little guy. It will only hurt... a lot!
Shoeshine Boy: [to Underdog] You're like Superman with a flea collar.
Shoeshine Boy: He says he thinks they should see other people. She says... Wait people eat that too
Shoeshine Boy: Destiny's a fumny thing. It'll creep up on you when you least expect it.
Cad: [after Shoeshine Boy sneezes on Simon Barsinister's face] Oh, gross! Your mouth was open.
Riff Raff: Aaaah! I'm naked!
Shoeshine Boy: There's no need to worry, Underdog is furry!
Dr. Simon Barsinister: [to the German shepherds] Bad dog!
Shoeshine Boy: There are no bad dogs, only bad owners!
Jack: It's time to teach you some manners.
Shoeshine Boy: Right. I'm going to learn manners from a guy who pees in my white porcelain drinking bowl.
Molly: You and your boss are not gonna get away with this!
Cad: He's not my boss, we're partners!
Molly: Well then, why are YOU doing this?
Cad: Because my partner would fire me if I don't.
Small Boy: Look! Up in the sky! It's a bird.
Woman: It's a plane.
Man: It's a frog.
Crowd: A frog?
Shoeshine Boy: It's not a bird, or a plane, or even frog. It's just little old me, Underdog.