As Kubla Khan says, a ring of conflict can be supremely useful, found in the text-based game NetHack. In particular, once you have one identified, you can easily kill large groups of monsters (e.g. a monster zoo or throne room) from anywhere in the level, without even needing to see them. Additionally, you can use conflict to kill a peacefull creature, say a shopkeeper or priest, without the usual penalties.

The bad news, however, is that you do not receive experience for creatures which you do not kill. Additionally, if a creature finds an offensive wand, it will likely use that to aid in killing its comrades, thereby using up the wand before you can stop it.