ToME WikiRegret: Cheerfully informs you, when you exit a level, of any artifacts you have left behind. "You just exited a level with the Long Sword 'Ringil' and the Power Dragon Scale Mail of Eternity!' Would not chime in for persistent levels, for obvious reasons. Probably should be cursed.
Fate Weaver: Gives you more fates and fates of greater significance (lower levels in the dungeon, more OOD items/objects, greater chance of death fates/cannot be harmed by mortal fates).
Traps: Cursed. Randomly generates traps around you with the message "Your foo of Traps trembles malevolently!". For extra meanness, make it instead blast you with random trap effects.
Violence: Every time you deal damage with a weapon, melee or ranged, it 'splashes' to random monsters in a 2 tile radius, including yourself. (Perhaps only melee?)
- Moebius Ring as a flavour. Or even as a kind of ring. 'The Moebius Ring evokes twisted, pretzel-like images in your feeble mind! You are confused!' Make sure their cousin the Klein Bottle is introduced too.
- Amulet of X-Ray Vision. Makes all terrain transparent and grants lite2.
- Artifact amulet, a stethoscope. Activates for probing, boosts and sustains con, regenerates, holds life
JohnGilmore: I really like the regret one. That's evil. It'd be better as a curse (non-item connected) which is either permanent or requires a special quest to get rid of. Better yet, for nasty rings/amulets, is to make them auto-pickup-equip-and-curse when you step on them. Obviously, that one would have to be an artifact, as doing that to a player more than once (well, alright, twice) in a game would be just too much. And if it's an artifact, a special quest to get rid of it makes even more sense, as a similar quest (the one ring) is the major point of the plot. Do a mini get rid of the cursed amulet of regret quest!
DarkGod: Yes nicely evil. Maybe with a message like "Ohhh no, damnit, you have JUST missed the wonderful Ringil! And you where just 5 squares away from it!"
Sirrocco: Even worse, of course, would be "And you were standing right on top of it, too!" and "And you had it in your hands!". I do thing it should be mocking, rather than false commiseration, though. Perhaps even with a mini-rumors file of its own for qutes to add on the end. "What's that? Can you hear it? Yup. That's Morgoth, breathing a sigh of relief." "Well, that's (number) alcove(s) in the Mathom-house that will stand forever empty. Thanks to *YOU*."
Orvin: I also really like the ring/amulet of regret. Here's another evil cursed one:
Myopia: Causes each monster (including uniques) the player is not adjacent to to look like a random non-unique monster of the same type. Not as bad as hallucinating, but not curable.
BitsySpider: It'd be nice to have "Drain Sanity" and "Drain GP" flags on items as well. Those could be curses in and of themselves, though draining sanity might be reserved for pretty deep objects since it's rather lethal to the unprepared. Draining GP is much less vicious, and might be good as an equivalent to the "of Teleportation" and such lower level curses. Speaking of Mathom Houses, it might be funny to have an ego type "of Legends" or somesuch that gives a bonus based on the number of artifacts in the Mathom House. Maybe pval = sqrt(number of artifacts in Mathomland). Might be amusing to have an "of Psychoceramics" or somesuch that gave bonuses based on the amount of cracked pottery in Mathomland.
PatashuPatashu: Heh, Regret was intended as an anti-Precognition. Instead of telling you what you can get while you can still get it it tells you afterwards. Anyway, few more:
Drought: Another cursed one. Drains fountains of their charges when on or adjacent, slowly dries up potions in your inventory and on the floor around you. However, it would grant water resistance and also dry up water you're beside.
Thorns: Shards aura and shard brands your weapon. 'Spiky vines lash out at your enemy!'
Translocation: Exchange places with any enemy you strike in melee or ranged combat (or the first one should you hit multiple opponents, with piercing or exploding ammo or whatever else might do it)
Tombstones: Any enemy you defeat will be replaced with a granite wall apon death, items shoved to safety. (Or not, perhaps?)