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.

Super Mario Maker
Grinders are set to reappear in Super Mario Maker. Their appearance is different from that of previous titles; they are larger and don't move if they are not connected to lines.