Special effect rooms are dungeon rooms with either a one-time effect on the PC or a permanent unique effect that affects the PC (or other monsters) as long as they remain on one of the tiles of the room. Any normal room on normal dungeon levels can be generated with a special effect (although it is unknown how other dungeon features like pools or forges overlap with these rooms).

Permanent effects[]

Permanent effect rooms can be identified by a message which is generated every time the PC enters the affected tiles. The set of effects is fixed and contains the following:

Room message Room effect
Strange lights flicker in this room. Every move inside this room causes the area around the PC (and on his/her tile) to darken if it was lit and vice versa. Methods of creating/removing darkness will not have a permanent effect in this room.
This seems to be a very dull room. Learning is negative trained (abused) while the PC is in the room.
The floor of this room seems to be very sticky. Energy cost for movement is increased by 30%.
There seems to be a shifting breeze in this room. Missile to-hit rating is reduced by 2/3.
The floor of this room is covered with puddles of ancient dried blood. Bleeding damage is increased.

You get the odd feeling that something is wrong with your perception of this room, but can't seem to tell what it is from just looking around.

Something is oddly wrong with the location you just entered although you aren't yet sure what it might be

Movement keys will propel the PC in the opposite direction. The result of Which direction? prompts for various actions is likewise reversed.
This room seems to be filled with a deadly and chilling silence. All sounds are muffled. Melee damage output for both the PC and monsters is multiplied by 10, causing tremendous amounts of damage. Very dangerous.
The air of this room is filled with the smell of carrots. Drinking a potion of carrot juice will permanently increase Perception by 1-5 points (+1c/ +3u/ +5b), regardless of potential. The room becomes normal after that.
The air in this room seems to be magically charged. Spells cost 20% less PP. This discount is not displayed in the spell list, and thus is not subject to the normal limitations on spell cost reductions; it can bring the cost of a spell lower than 50% of the spell's base cost.
The air of this room is filled with a very rich flavor. Satiation level of the PC doesn't go down over time. Doesn't affect actions that have an additional satiation cost, such as spitting acid, casting from HP, or eating stomacemptia herbs.
The walls of this room are made of many small stones of uniform height; they almost look like shelves of books. 50% less turns are consumed by each spellbook learning attempt.
This room seems to vibrate with life. Insects are crawling everywhere, strange mushrooms cover the walls and moss is growing at the ceiling. Melee damage output is divided by 10 for both the PC and monsters before PV calculations; may prevent the player from inflicting any damage at all.
This room smells of herbs and antiseptics. HP regeneration is faster (bonus HP point on each gain).
The air of this room refreshes you and sharpens your spirits! HP regeneration is much faster.
The aura of this room seems to be devoid of all life! PC's natural HP regeneration is stopped.
Hundreds of tiny insects are crawling beneath your feet and the whole ground seems to be covered with tiny white eggs! Breeding rate is increased.
The air in this room is stale in a highly unnatural way. Base PP cost for spells is tripled.
The atmosphere of this room makes your skin tingle! Base PP cost for spells is reduced by 20%.
This room seems to be incredibly ancient. Aging attacks (from ghosts, ghost lords and ghost kings) are more powerful (i.e. increase the PC's age by more years).
This room seems to be tainted by evil. Undead deal double damage.
You sense the presence of some supernatural entity of benevolent nature. Decreases prayer costs.
You sense the presence of some supernatural entity of malevolent disposition. Increases prayer costs (possibly 2x).

Unknown permanent effects[]

The following table contains a list of rooms with unconfirmed (from in-game testing) effects:

Room message Room effect
The walls and the ceiling of this room are sewn with cracks.
The walls of this room seem to be made from pure obsidian.
The walls of this room are covered with leering visages of demons of all kind!
The walls of this room are scarred with signs of many fights. Most parts of the room are heavily damaged.
The walls of this room are covered with ancient runes.
This room is very humid.
The skulls of many creatures are embedded in the walls. It's almost like being in the grave with them.

One-time effects[]

The rooms in this list apply one-time effect upon the first entering of the room:

Room message Room effect
Upon entering this room you feel a strange magical shock! PC loses all PP.
This room seems to be particularly unholy! Removes any temporarily-granted blessing that the PC has; only seems to appear when the PC has a temporary blessing.
Images of books and comfortable chairs line the walls. Suddenly the images fade away! -1 Strength, +1 Learning regardless of potential. If Strength is already at 1, then its potential may be lowered.
The walls have mirrors with many distortions of your image. You can't stand the sight of your warped self. All the mirrors shatter! Decreases Perception by 1 if Appearance is 18 or less; otherwise, increases Charisma by 1 regardless of potential. PC takes 1d4 damage. If Perception is already at 1, then its potential may be lowered.
The breeze accompanying you causes some ancient bones on the floor to transform into dust. You feel a sense of relief. Seems to, at least, restore one or a few hit points
This room looks like a spa with a mud bath. You are hit in the face by a glob of hot mud! Suddenly everything disappears! PC is blinded until they wipe their face; the blindness will never go away otherwise. The PC suffers a -1 penalty to Appearance while they have mud on their face. Wiping the mud off increases Appearance by 1 regardless of potential and removes the penalty.
A mouth appears on the wall and says... The rest of the message is a random fortune cookie message, succeeded by " and then it disappears."

Unknown one-time effects[]

The following table contains a list of rooms with unconfirmed (from in-game testing) effects:

Room message Room effect
A rat scurries between your feet and disappears in a small hole in the ground.
You notice a pale fading ball of light upon entering this room. It quickly disappears.
You hear an eerie wail for a few seconds...
You hear a strange "*TCHUNK*" in your vicinity.
For a few seconds you see a looming shade before you. It points its hand towards you in a threatening manner! Then it disappears.

Some information taken with permission from Andy Williams' Guidebook.