Ice Snake Block

Ice Snake Blocks are a type of Snake Block in New Super Mario Bros. Wii.

New Super Mario Bros. Wii
They appear in and function identically to normal Snake Blocks, but being made of ice, they are slippery and, throughout the entirety of the level, they move over a bottomless pit. The Penguin Suit, however, allows the player to move freely on the platform without slipping. Only two are found in the level: the first one that leads to the checkpoint, and the second one that leads to Lemmy Koopa.

Super Mario Maker 2
Ice Snake Blocks reappear in Super Mario Maker 2.

Trivia
Ice Snake Blocks were also originally going to reappear in New Super Mario Bros. U, along with a large variant, before being removed from the game