Bowser and company are going to secure the magical crystals from the previous game.
More of "bandicoot"'s familiar level design.
In the definitive version of these Classics the level design is more polished up to dissuade glitches. If you fall into a bottomless pit you come back up and go down a hitpoint rather than just dying.
There's also the local Bonus House per world you can peruse to restock your powerups.
