OK, after having a second look, J is the most interesting.
J: Those doors do lead nowhere in the material world, but are the portals that Mystifax used to summon his daemon thralls, and for which castle Daemondark earned its name. Mystifax was a distant ancestor of both Krako the necromancer and [enter name here], the current master of Daemondark.
The doors appear closed when the heroes enter, but spring open in a dramatic way before their very eyes when ever the game master sees fit. From now on, unholy things may come out of the portals at random, and closing them again is part of the heroes' objective. In every coming round, the gamemaster will roll two red dice for every portal in line of sight of at least one hero at the end of his turn. An unearthly beeing will appear according to table A and may move at once (but not attack this turn).
The heroes may enter the portals. Whenever a hero does so, roll a d6. 1-4: the hero passes through, 5-6: the hero is trapped in the void.
Passing through: The hero rolls 1d6. 1=1, 2 and 3=2, 4 and 5=3, 6=4. He counts the portals clockwise to this number to find the one he comes out. Seemingly there is no space in between.
Trapped: The hero wanders about in a featureless void. Every round he must roll 2d6. If the number is not higher than his mind points, he has found his way back. Else, roll another 2d6 to see if he encounters some inhabitants of this unworld. If yes, place all figures on a 4x4 room tile and fight out. The heroes must always fight alone, even if more than one is trapped.
To close the portals, the heroes must read the ritual on scroll X [please place it somewhere] and then close all doors at once (that implies that they must find a helper).
Table A:
| Out of portal | In the void | Monster |
| 1-7: | 1-5: | nothing |
| 8-9: | 6-7: | lesser daemon (looks and stats like a fimir) |
| 10: | 8: | greater daemon (looks and stats like a gargoyle, though it is not of stone of course) |
| 9: | 1d6 lesser daemons |
| 11: | 10; | lesser soul (looks and stats like skeleton) |
| 12: | 11: | greater soul (looks and stats like mummy) |
| 12: | 1d6 lesser souls |
Too harsh?