Creatures you have sacrificed may appear on the Astral Plane. Possibly, give the player a means of summoning them there as pets.

New monster “Phantom of War”, a powerful player monster style @ that appears on either the Astral Plane or elsewhere on the ascension run, but only if the player has successfully maintained pacifist conduct up until that point.

In an effort to remove the variance of randomly choosing the right or wrong altar on the Astral Plane: The first high altar you step on is always a wrong one, and the second one is always right.

Add 1-tile-wide corridors linking the rooms that contain the temples together in the Astral Plane, likely with secret doors so that monsters don’t start going through them. These give the player the ability to get around the Riders and go from the wrong temple to the correct one faster, but you run the risk of getting bogged down and surrounded if you use them.

It was pointed out that 1-tile-wide corridors may actually make things much easier on the player and would offer a much safer point to retreat to. Ideally they should be designed without long straight areas so the player can’t easily remove a bunch of monsters with a few well-placed teleportation zaps, but also be widened to avert the problem of being a refuge.

It is possible to leave bones on Astral. If this happens, instead of a ghost, there will be a fourth resurrecting Rider, War, with all the equipment of the dead player, 100% of it cursed.

If you kill a pet while on the Astral Plane (or the Plane of Air for that matter), you hear the rumble of “nearby” thunder, not “distant”.

Upon reaching the Astral Plane while crowned and with very high alignment record, you are granted a free artifact pair of gloves that give you an additional touch or weapon attack when worn.

Ringing the charged Bell of Opening on the Astral Plane aggravates every monster.

If someone steals the Amulet of Yendor and ascends on your altar, your god either still grants you immortality or at least an exalted position because after all, you did all the legwork getting it onto Astral.

Player monsters on the Astral Plane can be named after people on the top ten list (note that they don’t all have to be; some can use the same names they have now). Possibly, pick a different name if a player monster would be generated with the player’s own name, in order to avoid problems on single-user installs where everyone on the top ten list could have the same name as the player. Then again, that could be cool.

If Astral denizens are able to steal the Amulet from you and try to ascend with it: The amulet-bearer uses a special AI algorithm which pathfinds towards their high altar, using a shortest-path algorithm that avoids monsters if possible but if none are available will plot a path that goes through the minimum amount of monsters. They will only attack when the next square on their path is occupied by a monster, and they will only attack that monster.

If Astral denizens are able to steal the Amulet from you and try to ascend with it: Keep track of the god of the current amulet-bearer (whether you or someone else). Priests and angels aligned to that god grudge all others, and all others grudge them.

Remove/replace the guaranteed L and V monsters from Astral; the priests shouldn’t tolerate random high level undead hanging around.

The natural spawn rate of monsters on Astral (and perhaps the other Planes) is zero.

The Astral Plane should be brightly lit, what with having all the halls of the gods and being suffused with holy power.

Slightly bias priests’ and angels’ allegiances on Astral to be generated near their high altar so that the player can get a clue, but not enough so that it’s obviously distinguishable from random noise.

Replace all the priests of Moloch on the Astral Plane with (still hostile) priests of the other gods. Moloch is a disgraced, hated god, and his priests have no business there.

The hostile angels created on the Astral Plane by wearing conflict are immune to conflict.

The crossaligned high priests on Astral are hostile.

All Riders have intrinsic player-style MR, making them immune to death rays, but summon insects and summon nasties don’t work on the Astral Plane.

Hostile conflict angels don’t appear on the Astral Plane any longer, but all angelic and human beings are now immune to conflict on the Astral Plane.

Various alternate endings for the game:

• You can take over an abandoned shop, stock it with items and mimics, and settle down as a new shopkeeper, ending the game. This creates a bones file with you replaced by a shopkeeper bearing your name.
• You can eradicate the Wizard of Yendor from the game entirely and forever, becoming the next Wizard of Yendor yourself. This is done by standing in the center of the Wizard’s Tower wearing the Amulet of Yendor and invoking it. This respawns a beefed-up Wizard; defeat him and the game ends with you as the next Wizard. (It’s missing an end condition for what happens if you escape the dungeon while in this semi-powered-up state.)
• You can claim the Amulet’s power for yourself rather than giving it to a god. While anywhere on Astral, invoke the Amulet while wearing it. You get some big and unspecified surge of power from it. Furious at your betrayal, your god smites you every way they can, joined in by the other gods and the Riders, calling to bear all their priests, angels and Archons, which spawn in swarms on the high altars. (You also lose sanctuary.) You have to reach each high altar and shut it down/destroy it. Once you have done this, you win and keep the Amulet’s power for yourself, as long as you can manage to hold on to it.
• Alternatively, there is another way to do the “claim the Amulet for yourself” way: once you invoke the Amulet, a timer starts. The gods have only this much time to kill you or take the Amulet away before you become invincible to them. Would require some anti-boulderforting measures though. Or, you have to escape the Astral Plane back to the surface wiht all the gods trying to impede your progress.
• You want to break the power of the Amulet so no one gets it, and break the gods’ dominion over the world. You must invoke the Amulet while standing on each high altar to destroy it. (Not mutually exclusive with the other ending: you don’t channel the Amulet’s power into yourself, but into the high altar. In a game with both endings, you trigger the other one by invoking it anywhere except a high altar.)

Also see the Astral Escape Patch.

Peaceful priests and angels of your own god on Astral help you out by attacking hostiles. Possibly only if your alignment is good.

Revamp Astral so that the challenges to player mobility, options, and time don’t all depend on being crammed in by monsters. One idea is to have spellcasters that summon force fields / temporary walls to block your progress.