From the Super Mario Wiki
This article is about the obstacle. For information about other uses of the word, see Grinder
Grinders are metal discs found in some Fortresses and Castles of Super Mario World. 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, however, Spin Jump onto them, which lets them bounce off the Grinder without taking any damage.
Grinders re-appear in Yoshi's Story. They are abundantly found in Mecha Castle, 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.
Grinders in 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 goes on a certain part of the planet or passes the Grinder, it starts moving and any enemy that touches it disappears.
Grinders also appear in Super Mario 3D Land, behaving like they did in Super Mario Galaxy 2. They only appear in World 7-5, where they are the primary obstacles for the level.
Grinders appear in New Super Mario Bros. 2, where they operate as they did in Super Mario World. They can also jump vertically as well. They are among one of the few obstacles in the game that cannot be destroyed by the Gold Flower's fireballs.
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