Grinder

A Grinder is a spinning metal saw blade that acts as an obstacle in several Mario games.

Super Mario World
Grinders are found in some Fortresses and Castles in Super Mario World. In this game, there are two types of Grinders: line-guided and non-line-guided. The line-guided variety travels along a dotted line while non-line-guided Grinders travel across the floor. The blades are rather large and cannot be jumped on, although they can be defeated by a Slope Slide (which displays a glitchy sprite). Mario or Luigi can also Spin Jump onto a Grinder, which lets them bounce off it without taking any damage.

Super Mario Galaxy 2
In Super Mario Galaxy 2, Grinders appear in the Puzzle Plank Galaxy and the Rolling Masterpiece Galaxy, where they cut through planks of wood and cause them to fall. When Mario traverses certain parts of a planet or comes close to a Grinder, it starts moving and any enemy that touches it is defeated. The Prima guide refers to Grinders as Buzz Saws.

Super Mario 3D Land
Grinders also appear in Super Mario 3D Land, behaving like they did in Super Mario Galaxy 2. They appear only in World 7-5, where they are the primary obstacles for the level.

New Super Mario Bros. 2
Grinders appear in New Super Mario Bros. 2, where they operate on tracks as they did in Super Mario World. They can also jump vertically, if the tracks allows them to. They are among the few obstacles in the game that cannot be destroyed by Gold Mario's fireballs. There are also Big Grinders that appear in the game.

Yoshi's Story
Grinders reappear in Yoshi's Story. They are found abundantly in Mecha Castle and Lift Castle, and reappear in Magma Castle in tight spaces. Some Grinders are permanently connected to walls and need to be jumped or crawled past.

Paper Mario: Sticker Star
Grinders also appear in Paper Mario: Sticker Star. They are only found in Chomp Ruins where they will hurt Mario if he comes into contact with one.

Super Smash Bros. for Nintendo 3DS / Wii U
A Grinder appears as Bowser Jr.'s dash attack in Super Smash Bros. for Nintendo 3DS / Wii U.

Super Mario Maker / Super Mario Maker for Nintendo 3DS
Grinders reappear in Super Mario Maker and Super Mario Maker for Nintendo 3DS. Their appearance is larger and different than that of previous titles. Because Grinders didn't appear in Super Mario Bros. and Super Mario Bros. 3, new sprites were made for those styles, and the New Super Mario Bros. 2 model is reused for the New Super Mario Bros. U style, though a different sprite was created for the Super Mario World style instead of reusing the original sprite. They also cannot be Spin Jumped on safely (except with Yoshi or Goomba's Shoe) and are invincible. Grinders in this game remain floating in place if not connected to a track.

The version 1.30 update allows the player to shake the Grinder, turning it into a Bumper. The Bumper will simply cause Mario to bounce off it, and nothing else.

Mario & Luigi: Paper Jam
Grinders also appeared in Mario & Luigi: Paper Jam. They are found in Mount Brrr as obstacles in the Trio Drill sections. If the trio come into contact with one, they will be forced out of the dirt.

Super Mario Run
Grinders appear as obstacles in Super Mario Run. They can be found staying in one spot, or moving on a Track. Grinders appear in Cutting-Edge Spire and Make the Cut!.