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 sliding down a slope into them (which displays a glitchy sprite). Mario or Luigi can, however, Spin Jump onto them, which lets them bounce off the Grinder without taking (or causing) any damage.

They are seen in Super Mario Galaxy 2 in Puzzle Plank Galaxy, where they would cut through planks of wood and cause them to fall.