How do I make a wall that NPCs can't pass, but heroes can?
You do this with zones, which are areas of the map which you (invisibly) mark in the map editor's Zone Mapping Mode. You can define 9999 different zones per map, all possibly overlapping.
You can mark all the tiles that an NPC can't step on, and set that zone as the "Avoidance Zone" setting in the NPC editor (or as the default Avoidance Zone in the general map settings). Alternatively you can mark the only tiles which the NPC is allowed to step onto, and use the "Movement Zone" setting.
Or you can use both settings at once, useful if you want to reuse some general zones for different NPCs.
To create a zone, go to the Zone editing mode of the map editor, type in a number or press < and > to select a zone, press Z if necessary to switch from "Viewing" to "Editing" mode, and start adding/removing tiles to the zone by pressing SPACE. You can use a number of tools for drawing boxes and so forth.
Step-on NPCs[edit]
A more difficult alternative method is to create a wall of invisible NPCs (with blank pictures), since NPCs won't step on each other. Change the Activation type of this invisible NPC to be "Step On", but do not actually choose a text-box to be displayed. This means that the hero can step on the invisible NPC, but the NPCs will not be able to.
You can place several copies of this invisible NPC on the map, forming a wall that the hero can pass but the NPCs cannot.
