Morton Koopa Jr., or simply just Morton, is the boss of the second world in Super Mario Bros. 3 and Super Mario World respectively. Morton is depicted as the "average" Koopaling, usually possessing no noteworthy special abilities or quirks. He is also a bit of an oaf. His abilities are similar to Roy Koopa.
In the cartoons he was named Big Mouth Koopa, ostensibly because he was more talk than action, and as an homage to Downey, whose entire theme was his admittedly big mouth. His show’s logo was a large open mouth, which Morton/Big Mouth Koopa’s design even resembled. Aptly, in the Super Mario World cartoon, he occasionally served as an announcer (until an annoyed sibling or Koopa would stop him when he talked way too much). There are a few physical differences between Morton and Big Mouth: Morton’s shell is gray (or black in New Super Mario Bros. Wii) and Big Mouth’s is purple; Big Mouth has much larger eyes and purple eyelids; and the star-shaped birthmark (a possible reference to Paul Stanley from the band KISS) on Morton’s face is darker around the cheek, while it’s just one solid color on Big Mouth. Morton Jr. is also much larger than Big Mouth. In the Super Mario World cartoon, Big Mouth’s shell became the same color as in the artwork shown on the side.
Heavy Weight Jump: Morton can jump and pound the ground with great force due to his weight.
Magic Wand: Like many other Koopalings, Morton can use his wand to create pink magic blasts. However, in New Super Mario Bros. 2, he creates instead spike balls.
Hammer Blitz: With two segments of a Pokey left, Morton will strike them faster making them hard to dodge.
Morton is the only Koopaling to sport a gray shell. Wendy's shell is pink and Roy's formerly; Roy's is currently Purple and the others all have green shells (in the unused Super Princess Peach sprites Wendy was the only Koopaling without a green shell). Morton has a black shell in New Super Mario Bros. Wii.
Morton was named after American talk show host, Morton Downey Jr. This name was chosen because Morton "looked like a loudmouth" much like Downey. 
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