The Mushroom Kingdom stage has three warp pipes. Two of them can be entered, and the character which entered it will appear in one of the two others randomly, though if one is blocked, they will always come out of the other.
Luigi's Target Test stage also features large platforms based on Warp Pipes.
In SSBM, Warp Pipes commonly serve as platforms, such as in Yoshi's Island: Yoshi's Island.
In Mushroom Kingdom Adventure, they also serve as "checkpoints," in that if the player dies, they will re-spawn at the last Warp Pipe they passed.
There are also three that appears in the background of Mushroom: Kingdom, and another three in the platforms.
In the background of the Mario Circuit, various Warp Pipes can be seen.
Lastly, they appear as obstacles on the stage Mushroomy Kingdom.