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 "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 gear 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 slight visual changes, having eyes inside visors instead of a face. Besides appearing in the aforementioned worlds, they also appear in the Battle Fort stage.