Rotating events.

[Danny]

Through events and layers mostly, but if I am correct, there are a few ways to do it with the Attach to Layer setting?

[bossedit8]

Use a Layer on a Block that you want to rotate. Then make a Roto Disk or Firebar that "Attach" to a certain Layer that you want to rotate. After you finished everything on your level and layers make the roto disk or firebar invisible.

[Chad]

Use the Roto-disc/Firebar method carefully though, because platforms attached to them are really hard to stand on and jump off of. You should probably minimize hazards around them and such. Movement events would be more stable, but you'd need to make long list of them with slightly different directions that eventually come together in a loop. Whichever method works best for you.