The potion is a door, not a warp map
Sub-space is the dark copy of the current area you enter through a Magic Potion door. It is how this game hides coins and extra health. It is not Super Mario Bros. 1’s Warp Zone.
What the potion does
The NES instruction booklet: throw a Magic Potion to create a door to Sub-space. Walk through that door. That is the whole mechanic. If you throw it off-screen or in a useless spot, you waste the door.
CONFIRMED — Super Mario Bros. 2 NES instruction booklet (Magic Potion / Sub-space)Why / when
The booklet says entering Sub-space turns grass into coins until the magic is used twice in an area, and a heart may appear that increases the life meter. Use a potion when you can throw it next to grass you still need, or when you want the heart. Do not save every potion “for later” if the area is about to end.
CONFIRMED — NES instruction bookletTwice per area
The booklet’s “until magic is used twice in an area” cap matters. A third potion in the same area is not documented here as extra coins. PixelQuest is not inventing a hidden third-use rule.
CONFIRMED limit — NES booklet; extra uses = UNKNOWNNot in this page
PixelQuest is not publishing a complete potion-spawn list or a warp-vase coordinate list this batch. Those are high-intent only if every location is source-locked to this USA NES version.
NOT SHIPPED — location farm deferred