Red POW Block

Red POW Blocks are a red variant of POW Blocks that much like the blue type, they cause an earthquake effect on screen. However, these do not damage enemies or drop any coins, but instead break and hit blocks and can start chain reactions if another Red POW Block is in range of the effect.

There has been instances of POW Blocks being colored red in other games, such as Super Mario Bros. 2, although it's worth to note they behave just like normal POW Blocks do, while these are classified as a different variant with distinct effects, rather than just a change in color.

New Super Mario Bros. 2
Red POW Blocks first appears in New Super Mario Bros. 2, and is the only POW Block variant that makes an appearance. They cannot picked up, so they must be activated by hitting them normally. In addition, they start a chain reaction with one another when activated; while they cannot defeat on-screen enemies out of its range or drop midair coins, their tremors can hit nearby blocks.

Super Mario 3D World / Super Mario 3D World + Bowser's Fury
Red POW Blocks reappear in Super Mario 3D World and its Nintendo Switch port, which marks their first appearance in a 3D Super Mario platformer. They act exactly as they did in New Super Mario Bros. 2, releasing short-ranged shock-waves that hit and destroy blocks and enemies once hit. They can also reveal the locations of Hidden Blocks.

Super Mario Maker 2
Red POW Blocks reappear in Super Mario Maker 2, albeit only in the Super Mario 3D World style and instead behaving like it did in New Super Mario Bros. 2, so the locations of Hidden Blocks do not get shown anymore. Version 3.0.0 introduces Red POW Boxes, wearable Red POW Blocks that activate upon hitting blocks three times before vanishing, and just like the actual block, it is exclusive to the Super Mario 3D World style.

Trivia

 * In the Super Mario Mash-up in Minecraft, TNT is replaced by Red POW Blocks.