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.

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.

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.

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 rails as they did in Super Mario World. They can also jump vertically, if the rail allows them to. They are among the few obstacles in the game that cannot be destroyed by Gold Mario's fireballs. There are also larger versions that appear in the game.

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
Grinders reappear in Super Mario Maker. 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. They also cannot be Spin Jumped on safely (except with Yoshi) and are invincible. The 1.30 update allows the player to shake the Grinder, turning it into a Bumper. The Bumper will simply cause only Mario to bounce off it, and nothing else.