There are a lot of beta elements that appear in Super Mario 3D World. The first thing is that the game was orignally called New Super Mario 64 Wii, it was changed due to it being a long name.
A lot enemies were going to be found in the game but were either replaced or just taken out. King Bills were going to appear in a few courses but it was taken out due to lagging. There were going to be Tail Buzzy Beetles but didn't appear, probably because of to many Tanooki tailed ememies. Also Tail Koopas appeared but they acted just like the Tail Buzzy Beetles.
The first level, Rolling Greens, was going to be the 3rd course to be unlocked but was changed because it was very basic. It was also called Rolling Greens Terrace but was changed to Roliing Greens.
Molten Magma Land had a few changes in design and texturing.
There is a beta course which featured colorful blocks and water. It looks very similar to the first level in Super Mario 3D Land. It was originally the first course of the game but was taken out due to it being small and it only had one Power Star. If the course was played by hacking the game it is very glitchy and when collecting the Power Star the game will freeze.
Luigi had a Power-up that turns him into Tornado Luigi. He was able to throw 3 mini tornadoes at a time. They acted like Boomerangs but they homed in on an enemy. They would come back to Luigi so he can throw them again. This was taken out since it was weaker and would only make the enemy dizzy.
The Hammer Suit and Boomerang Suit were suppose to look like the Hammer Suit from Super Mario Bros. 3 but were changed to look like the Boomerang Suit in Super Mario 3D Land. This was changed since it is a sequel to the game Super Mario 3D Land.
The Rock Mushroom and the Cloud Flower were going to appear in the game but only the Bee Mushroom appeared from the Super Mario Galaxy series. Also the Spin Drill never appeared originally. The way to turn Mario or Luigi into Metal was by getting a Metal Cap, but it was changed to a Metal Mushroom for unknown reasons. Poison Mushrooms were able to kill Mario or Luigi, but it was changed to making them in Small Form.