Add a quiver item. Ostensibly in the tool class, could either take up a new equipment slot, or take up the shield slot to prevent you from wearing a shield at the same time the quiver is equipped. It’s not actually a container, and just “holds” whatever is in your existing in-game quiver. While equipped, it adds +1 to your multishot, possibly +2 if it is blessed but this may make it too powerul.

Also change the Ranger quest artifact to the Quiver of Diana, a quiver which gives telepathy and reflection when equipped and possibly also prevents ammo from breaking, though it can still erode. When invoked, all projectiles on the level that you threw or fired are magically returned to your inventory, even if they’re being carried by monsters or buried or whatever.

Player monsters who spawn at a certain depth have a very low chance of generating carrying their quest’s artifact. This chance is highest when deeper than the Castle, but is still low.

Any quest-artifact-stealing attack has to pass an additional roll to work successfully if you currently have the artifact equipped.

The quest leader either sometimes or always asks for the quest artifact back when you return with it, to replace the weird flavor in most quests that the leader is desperate to get the artifact back but is then completely fine with you adventuring off with it after retrieving it.

If you refuse to give them the artifact back, they turn hostile. If it’s a chance-based system, the chance might be dependent on your alignment record, so a character that has misbehaved is less likely to be found worthy of keeping the artifact. However, since you must have +20 alignment to enter the quest and get a massive amount of alignment from killing the nemesis, it’s questionable whether anyone’s alignment will ever be in a bad enough state to increase the chances. Luck has also been suggested as a variable that influences the chance, but most players will already have maxed their luck by the end of the quest.

In order to keep the player from just dodging the quest leader on their way out of the quest so that they can keep the artifact, various enforcement mechanisms have been proposed:

• Incentive-based; returning the artifact gives you +5 alignment record (and set to 0 if negative) and +3 to luck. Rewards should be better than the incentive of killing the quest leader to get the artifact back, or else penalties applied if you kill them (e.g. the artifact blasts you even though it’s your own quest artifact).
• Strict: you must show the artifact to the quest leader and have the quest marked completed in order for the invocation to work. Alternatively, the quest leader has the Bell of Opening and will only surrender it when you present the artifact, whether or not they demand it back. Or the quest nemesis has cursed the Bell and the leader will lift the curse after you show them the artifact.
• Delayed: you don’t have to go without the artifact forever, but the leader demands it back for some time so that they can fix whatever problem the artifact needed to solve. This could manifest as either a variable number of turns, or a requirement to go explore a certain number of new levels/area, before they’re done with it.

All quest artifacts, even coaligned ones, will evade your grasp if you have not yet finished the quest. This is because they refuse to be handled by someone who hasn’t yet proven themselves.

Replace Cavemen’s quest artifact with scales from the Chromatic Dragon (their quest then becomes “kill the dragon that is terrorizing our people” instead of “fetch the artifact from the dragon who stole it”). The scales only drop when she is killed, rather than her being generated with them (thus, they can’t be stolen). The scales could either be implemented simply as a base item akin to chromatic scales in UnNetHack which provide a cocktail of resistances, or as an artifact. If implemented as a non-artifact, the Caveman role will have no associated quest artifact.

The scales should NOT be enchantable into scale mail. The pile of resistances is good enough.

Instead of the Wizard of Yendor stealing all quest artifacts, he can only steal ones that don’t belong to your role, since you didn’t actually earn them.

Change the Ranger quest artifact to an infinite quiver that can produce an endless supply of arrows, rocks, or crossbow bolts, preferring to match to whatever the hero’s wielded weapon is. This benefits gnomes who want to use crossbows.

Make Big Stick (Caveman quest artifact in Fourk) deal two bonus attacks which may or may not hit (but it still all appears to be one hit). If both bonus attacks hit, the target is stunned and confused.

If you get another role’s quest artifact through bones or wishing, player monsters of that role will gradually start to be spawned of increasing difficulty who pursue and hunt you down because you are now their quest nemesis.

Change the Knight quest artifact to be the Holy Grail. When quaffed from, something good happens; perhaps it needs to have charges or invoking it fills it up so you can drink from it (and you don’t have to drink from it immediately, allowing strategic choices). Should give magic resistance when carried. Possibly gives the effect of a random potion when quaffed: always a “good” potion when blessed, a random one if uncursed, and a “bad” potion if cursed. Or it blesses items dipped into it.

Quest artifacts, and probably all artifacts, blast other monsters when they enter their inventory, subject to the same checks and chances as the player (however, the artifact will never evade their grasp). This is most likely to be observed when a quest nemesis or the Wizard of Yendor steals a quest artifact from the player.

Make the Ranger quest artifact a crossbow if you are a gnome.

The Bell of Opening is carried by your quest leader, who gives it to you when you return to them with the quest artifact. This solves the problem of making a game unwinnable by permanently changing alignment, since you can also get it by killing the quest leader. Should the leader leave the level (by levelporting down, for example), they are considered derelict of duty and the player can start the quest.