From the Super Mario Wiki
A Crazed Crate is a beige box with the same worried face on each side of it. If Mario grabs a Crazed Crate, the box bounces around three times in the direction Mario is facing, with the plumber holding on. The jumps get progressively higher. After the last jump, the crate explodes and a few Coins appear. Crazed Crates can also bounce off of walls, which will not count as one of the three bounces. Crazed Crates appear in Big Boo's Haunt, Tall Tall Mountain, Lethal Lava Land, and Shifting Sand Land. In all levels listed, only one appears, except for Shifting Sand Land, where there are two.
Many Crazed Crates also appear in a Mario Party minigame called Box Mountain Mayhem where a player has to break all crates to get Coins; however, if he or she gets a Crazed Crate, the player does not get a Coin and may be unable to move for some seconds. These crates are called Whomp Boxes.