There should be some way to enter the Valley of the Dead without requiring fighting through or looping around the Castle, in order to allow a player struggling to get up to the Quest experience level threshold to access the resources in the Valley.

The room of gems in the Castle should never contain worthless glass. (Unspecified whether it should still contain gray stones, or exclusively valuable gems.)

Change the game progression significantly so that the player cannot descend below the castle without all the invocation items; once they do, they must perform the invocation at the Castle and fall directly into Moloch’s Sanctum. Exploring Gehennom after that is therefore done for the first time and from the bottom up.

The castle chest containing the wand of wishing requires a special unique key to open (it can’t be opened any other way). The key is carried by a random lieutenant or captain generated on the level.

Add gargoyles (or statues of gargoyles) to the Castle.

Remove the graveyard flag from the Castle level, but make it so that undead cannot follow you upstairs past the Valley of the Dead, preventing wraith luring. (Could also apply this restriction to levelport and branchport).

The passtune can be played at any drawbridge in the game to open or close it, but only the Castle drawbridge gives feedback in the form of gears and tumblers. You have to learn the passtune there in order to feasibly use it at other places.

Before you first enter the Valley, demons and undead (chosen from the graveyard monster algorithm, though perhaps excluding wraiths) continually spawn in the maze on the right of the Castle and try to path towards the upstairs. Also before it is set, in the Valley, awake demons and undead will try to path to the upstairs if they have nothing better to do.

Add a guardhouse to the Castle outside the immediate drawbridge area containing some soldiers and sergeants, where the player might find a bugle with which to play the passtune.

Make the Castle a side branch, putting two down staircases on Medusa, one of which goes to the Valley and the other of which goes to the Castle branch, first preceded by several maze levels.

Make the Castle not a graveyard level, and compensate for this by altering wraith corpse drop odds somehow.

The three unoccupied corners of the Castle contain mimics mimicking chests.

Make the Castle barracks have second doors that open onto the courtyard.

In the last level of the Dungeons of Doom (normally the Castle), the powers of your god and Moloch are approximately equal, and prayer may or may not work here. (The Valley is strictly Moloch’s territory.)