World 2-3 (Super Mario Maker for Nintendo 3DS)
From the Super Mario Wiki
Because of the mechanics of Super Mario Maker, it is just long up and down tracks with a lift going down on each one. Also, short versions of each world replace their respected worlds. In each one, the player must find a key and open the locked door. However, it appears that in world 4, it is possible to leave it, but not without getting the key because it is in a Lakitu. The other keys are out in the open and in a Question Mark Block in 3 and 2 respectively. The only enemies not in the original 1-2 are the aforementioned Lakitu and two Koopa Paratroopas.