World 1-3 (Super Mario Bros. 2)
The level features a hidden warp to World 4. Right before the castle, there will be a cluster of plants, one of which is a Magical Potion. The player must take the Magical Potion past the castle to a jar. Then player needs to use the Magical Potion to create a door; once through, they can enter the jar while still in Subspace to warp to World 4.