Double Item Carry
In SMW, you can carry two items at once, such as a shell and a p switch, 2 switches, multiple springs, on and on. This isn't required in many kaizo levels outside of hacks that utilize glitches, but it can be used to cheese certain levels in both kaizo and non-kaizo hacks. You utilize this trick by placing one item down, then placing the other item down on top of the first item, one pixel apart. If done correctly, Mario will pick up both items and carry them.