Good editor that does almost everything you ask for. There is only one thing I can think of that it can’t do and this is: make use of the extra room layouts which are shown as garbled graphics.

This isn’t actually layout data. It is the data that is used to build the columns used in the layouts. Those are stored right behind the room layouts. Moving those away and repoint them to the free space at 0×16C5A would open up 20 more room layouts (the last 2 are staircase layouts which you also can’t edit with Dungeon Master) and more space to build columns.

Sadly Dungeon Master expects this data at the original address, so if you move and repoint it, the game would work fine, but Dungeon Master would show garbled room layouts or crash, making it very hard to build dungeons with it.

I hope this get’s included in a future update at some point. Support editing the columns or actually read the pointers for the columns at 0×16714 instead of always looking at the original place, which would be used by the additional layouts and crash Dungeon Master or show nonsense.

If you don’t intend to have more variety than the original game had, this editor is perfect. Otherwise you need to use a hex editor.