The POW Block is a recurring item in the Mario series. It appears with similar effects in each game it appears in. When struck, it knocks over all of the enemies on screen that are currently touching the ground or a platform. The POW Block has a limited number of uses and shrinks with each hit it receives. In most games, these blocks can be picked up and thrown, and some are required to obtain a 100% game completion. Most of these blocks are blue in color, but some appear red. Each variation of the block features the word "POW" on one side, all in capital letters.
The POW Block marks its first appearance in Mario Bros.. Two are featured during each phase. When the player hits one, it shakes the screen, causing all enemies on a platform to be knocked onto their backs. The block can only be struck three times before it disappears completely. Each time the player strikes the block, it will flatten down quite a bit.
In the GBA version, the block can also be picked up and thrown, but throwing it will cause it to disappear completely, regardless of how many times it was previously struck.
The POW Block reappears in Super Mario Bros. 2 as an item that is able to be picked up and thrown at enemies and the ground. When they are thrown, they cause an earthquake that kills the enemies on the ground.
"Flips shell enemies and inflicts 2 damage points on all enemies."
The POW Block is also one of the many items featured in the Paper Mario games. It is a purchasable item from some early stores in all of the games, although usually it is the second store that sells it. POW Block is an item that deals two damage to all of the enemies on the ground and on the ceiling in Paper Mario and The Thousand-Year Door. In Super Paper Mario, oddly enough, the POW Block causes minor damage to all enemies that are on the screen, including flying enemies as well. In Paper Mario: Sticker Star, POW Blocks return as Stickers. Unlike the previous Paper Mario games, Mario can hit the POW Block twice with the Action Command to do damage to all enemies. There are also Shiny POW Blocks and Flashy POW Blocks.
In Mario Kart Arcade GP 2, the POW Block appears as a special item for Waluigi. When used, it causes an opponent to be stunned for a short amount of time.
In Mario Kart Wii, the POW Block hurts all enemies ahead of you, but spares those behind. When fired off, it'll count down slowly through three stages prior to impact, at which point your enemies will all spin out to much calamity and amusement. If on the receiving end, use its advanced warning to immediately grab some air, as the POW Block only damages those on solid ground. Unfortunately, meager hopping won't be enough. The POW Block can however be avoided by shaking the Wii Wheel (or initiating the controller's "trick" button) immediately when the Block reaches its smallest size. You could also wheelie hop, but you have to have a bike. You will lose your items and spin uncontrollably, but you will not lose any speed. If successful, blue circles will appear underneath the kart or bike. It can be avoided in midair.