Vanilla 1UP point checkpoints:
Super Mario World has four 1UP checkpoints objects. They don't appear if you already collected them all in a level (even if you die), so they can be used for checkpointing. Essentially, you can hide blocks (for instance warp pipes) by putting 1UP checkpoints over those. Then, when time comes you can guarantee getting 1UP checkpoint (by putting multiple 1UP checkpoints in a row).
Display Level Message 2:
Put two Display Level Message 1 sprites in the same place.
Inverse switch palace blocks:
To be written, but I somehow managed to do that in vanilla (hint: bottom tiles of palace switches are solid, the object doesn't appear when switch is already pressed, so you can put something below it).