From the Super Mario Wiki
Heave Hos are red mechanical enemies in Super Mario 64 and Super Mario 64 DS. Heave Ho's name is a pun on the phrase "Heave Ho!" which people would say when trying to move something. They appear in Tick Tock Clock and Wet-Dry World.
They ride on three wheels, and have a dustpan-like mechanism with footprints on it, which they use to fling Mario upwards. On the Heave Hos' sides are emblems of Bowser giving a thumbs up, which is over the word "KOOPA" written around in fire. After moving around their area, they lose power, and they have to wind up the key-like object in their backs, much like a toy.
Heave Hos can help Mario by flinging him upwards depending on the direction they are facing to help him reach higher areas. More often than not, they are a hinderance, as the height at which they toss Mario is such that he will take fall damage upon landing (unless he lands on a higher area); this is especially dangerous if he is thrown into a lower level.
In Super Mario 64 DS, Heave Hos underwent multiple visual changes, having eyes inside visors instead of a face. The "KOOPA" emblem is gone from their texture. Besides appearing in the aforementioned worlds, they also appear in the Battle Fort stage.