From the Super Mario Wiki
The Penguin Suit is an item found in the game New Super Mario Bros. Wii. As the name suggests, it is a suit that resembles a penguin. This item first appears in World 3, and from then on it can found in Toad Houses as well. The suit allows players to turn into their Penguin form, that has a blue or black body with short, colored trousers. It also gives players the ability to throw Ice Balls at enemies, freezing them (just like the Ice Flower); allowing the frozen enemies to be used as platforms. It also improves traction, making players not slip while on ice. In addition, the Penguin Suit lets players swim more efficiently underwater, and even slide on ice and water without sinking or breaking any blocks they collide with. It is also able to defeat enemies, but will bounce off a sliding Cooligan or a Piranha Plant unhurt. It is introduced along with the Propeller Mushroom as the newest power-ups in the game.
The Penguin Suit reappears in New Super Mario Bros. U and acts the same way it did in New Super Mario Bros. Wii, though the player must get it through a Power-Up Toad House in Superstar Road. Additionally, Penguin Bowling allows use of the Penguin Suit. It can also be used in the Penguin Pack from Boost Rush Mode. In the expansion pack, New Super Luigi U, the Penguin Suit made more frequent appearances in courses including some outside Superstar Road.
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