
Both worlds have a non-scrolling underwater level ( World 3-3 and World 6-5), before another level that introduces new enemies ( World 3-, which introduces Boo]s and Splunkins, and World 6-6, which introduces Chain Chomps) before going to the Castle, if taking the main path. For the first Tower and the Castle in World 6, said enemies and obstacles are swapped around. In a strange parallel, the Tower and Castle in World 3 prominently featured Koopa Troopas, and Skewers with Dry Bones respectively. Additionally, there are two main levels and the unlockable level before the Tower. On both overworlds, the player can choose to start with either the first levels or an unlockable level.
World 6 can be considered to be the mountain-themed counterpart to World 3.