Covetous

Certain high-level monsters are covetous, in that they will try to steal one of the unique items, or your quest artifact. The quest artifacts of other roles are immune from this theft, as is yours if it is stashed in a bag. There is no defence against this theft for items in your main inventory; this is especially troublesome if your only source of magic resistance is your quest artifact.

Item	Coveted by
Your quest artifact	All quest nemeses
Candelabrum	Vlad
Book of the Dead	Orcus, Master Lich, Arch-Lich
Amulet	Asmodeus, Baalzebub, Demogorgon, Dispater, Geryon, Juiblex, Orcus, Yeenoghu
All of the above	Wizard of Yendor

On one-twentieth of the hits from such an attack, the monster will look for one of the above items in your inventory; if it finds one it will steal it and, if capable, teleport away.

The Wizard of Yendor is most notorious for this; if he casts double trouble, his double has a chance of carrying a cheap plastic imitation of the Amulet of Yendor which can be confused with the real amulet if it is stolen.

Behavior

Covetous monsters do not deign to walk from place to place as other monsters do. When a covetous monster wants to attack, he simply appears adjacent to you, or as close as he can get if there's no open space next to you. This type of teleportation is not influenced by non-teleport levels.

A damaged covetous monster will teleport to the up stairs to heal. The damage does not need to be critical; even a few HP lost will send it fleeing. While healing, the monster may occasionally appear for a quick attack or two before returning to the stairs. It will not resume a sustained assault until fully healed.

If you pursue a covetous monster to the up stairs, it will escape to the level above. When you follow, it will immediately teleport to the new up stairs to continue healing. You may end up chasing it all the way to dungeon level 1 (monsters cannot escape the dungeon entirely).

Covetous monsters ignore Elbereth when teleporting to the up stairs. They follow the normal rules for respecting Elbereth in all other situations.

Strategy

Because they flee at the slightest scratch, are much more mobile than most players, and are invariably high-level and so have a lot of hit points, covetous monsters can be very frustrating to deal with. The easiest option, if you have teleport control, is to teleport to the up stairs before the monster does. If the monster respects Elbereth, engrave it, and you can safely dispatch the monster when it follows. If not, you have at least cut off its escape route and forced it to fight you to the death.

If porting to the stairs is not an option (because you lack control, are on a no-port level, or another monster is already on the up stairs), but the monster is a Follower, you could also flee to the down stairs, head down when the monster is next to you, and hope you land on the up stairs.

Source code

Covetous monsters are defined by one of the following flags in monst.c: M3_WANTSARTI, M3_WANTSCAND, M3_WANTSBOOK, M3_WANTSAMUL, or M3_COVETOUS.

There is also a M3_WANTSALL flag. It has the same value as M3_COVETOUS, but is not used by any monsters. It seems likely that M3_WANTSALL was intended to indicate monsters that are capable of stealing all of the major items, whereas M3_COVETOUS was intended as a mask to check if a particular monster is capable of stealing at least one major item. If this is the case, the Wizard of Yendor should be specified as M3_WANTSALL instead of M3_COVETOUS. However, since the two symbols have the same value, the mistake does not actually affect gameplay.