Madness Effects

GM note

Like with horror, these are the madness effects that I picked out from the 3e Ravenloft Campaign Setting and Pathfinder Horror Adventures because they seemed relatively interesting and fun to play and were pretty well balanced with each other. If there's another effect that I didn't include that you think would be appropriate, let me know, because your definition of "interesting and fun to play" might be different from mine. And again, I'm open to nonconventional ways to run these.

Minor Madness Effects (roll d4 or choose)

Minor madness effects come into play when you fail a madness save by 1-5 points.
Blackout (1): The character is merely shaken at first. However, they will not recall the scene that prompted the madness save or anything for the following 1d6 hours. Spells such as modify memory can restore these lost memories, but recovering the scene that prompted the madness save will prompt another madness save at the same DC.
Denial (2): The character's mind refuses to accept the existence of the threat that prompted the Madness save. For 1d6 hours, they act as if the threat simply does not exist. Denial provides the character with an effective +4 insight bonus to any Will saves against that threat's attacks, but otherwise offers no protection.
Horrified (3): The character suffers a moderate Horror Effect. This Horror effect lasts only 1d6 hours, rather than the usual two weeks. (In the case of Nightmares, it lasts only for the night following the failed save.) 
Unhinged (4): The portion of the character's mind that should have gone mad simply shuts down instead. This leaves the character able to function but affects their personality. They receive an effective +2 morale bonus to all Fear and Horror saves, but their alignment temporarily changes (roll 1d8 to randomly select a new alignment, omitting the character's original alignment from the options). The character regains their normal alignment (but loses the morale bonus) after 1d6 hours.

Moderate Madness Effects (roll d4 or choose)

Moderate madness effects come into play when you fail a madness save by 6-10 points.
Delusions (1): The character believes something about themself or the world that simply is not true. The nature of this delusion is usually tied into the event that provoked the save. Examples include believing that they have become a supernatural creature, that a specific person is in love with or wants to harm them, or that they or another person is actually someone else. The character can perform actions only if they can rationalize them within the context of their delusion. For example, a character who believes themself to be a vampire would not be willing to expose themself to sunlight.
If a character ever performs an action that should be impossible within the context of the delusion, the character must make an immediate Horror save.
Depression (2): The character is overcome by a deep melancholy and pessimism. They often come across as quiet and withdrawn, wanting mainly to be left alone. The character takes a -2 penalty on Initiative checks, and any morale bonuses are halved. The character also has trouble focusing their thoughts through the haze of depression; they take a -2 penalty to Intelligence and Wisdom-based checks, and must succeed at a DC 16 Will save to take 10 or 20 on any check. One benefit, however, is that the character’s withdrawal leads to a +4 bonus on all Fear, Horror, and Madness saves.
Hallucinations (3): The character perceives something in the world that simply does not exist, usually related to the source of the madness. The hallucinations function like illusions, except that the character is both the caster and the subject. A menacing hallucination might provoke a Fear or Horror save and can even attack the character, although it only inflicts subdual damage (the character merely believes they are being harmed).
A character may try to disbelieve the hallucinations as a standard action (Will save DC 13+character’s Wisdom modifier). If the character succeeds, the hallucination does not necessarily end, but it can’t provoke Fear or Horror saves or cause subdual damage.
Paranoia (4): The character believes that they exist at the center of a conspiracy dedicated to their destruction. They gain a +2 bonus against charm effects, but take a -2 on Bluff, Diplomacy, and Sense Motive checks. The GM rolls all Sense Motive checks in secret for the character; failure gives the impression that others are plotting against them. The character also has trouble trusting their allies, and must make a DC 16 Will save to benefit from the aid another action or to accept a beneficial spell or effect from an ally.

Major Madness Effects (roll d4 or choose)

Moderate madness effects come into play when you fail a madness save by 11-15 points.
Amnesia (1): The amnesiac character immediately blocks out all memory of the maddening event—along with many of the months or years that came before it. Roll d% and multiply this percentage by the character’s total levels (rounding down). The character receives that many negative levels. An amnesiac character has access to all their skills, but loses all memory of events since gaining those levels. A character who acquires negative levels equal to their character level regresses to childhood. Restoration spells cannot remove these negative levels.

Dissociative Identities (2): The character’s psyche attempts to protect itself by splintering into 2d6 additional identities. Work with the GM to create appropriate personalities for alters, or allow the GM to roll them randomly. Alters have access to all of the core personality’s skills and abilities, but they will not use them if doing so is out of character (i.e. a fighter alter won’t cast spells). Whenever a character suffering from Dissociative Identities has to make a Will save, they also have to make an immediate additional Will save equal to the failed Madness save’s DC or randomly switch personalities (as a free action). The character should also make a Will save (DC 15+ character’s Wisdom modifier) each time they rest. If the character succeeds at the Will save, they wake up as the core personality. If they fail, they switch to a random persona.
The core personality has no conscious memory of time spent in other personalities, but does gain XP normally. Alters may or may not be aware of each other; if they are, they can “leave messages” for each other.
Psychosomatic Loss (3): While there is nothing physically wrong with the afflicted character, some kind of mental trauma has forced their brain to shut down sensory or motor systems. The character becomes blinded or deafened, loses another special sense (like scent or blindsense), loses the use of limbs, or uses a special movement speed (like a fly or swim speed). Magical effects that typically remove these conditions (such as remove blindness/deafness) have no effect.
Schizophrenia (4): The character’s personality suffers a serious collapse. As their sense of self erodes, they can experience drastic and unpredictable personality shifts. Whenever the character has to make a Will save, they also have to make an additional Will save equal to the failed Madness save’s DC or have their alignment immediately and randomly change. The character should also make a Will save (DC 15+ Wisdom modifier) each time they rest. Failure indicates that their alignment randomly changes upon waking.

Catastrophic Failure

If a character fails a Madness save by 16 points or more, their mind is shattered. They suffer a major Madness effect and lose 1d6 points of Intelligence, Wisdom, and Charisma.

Treatment

As with horror effects, a character may make another saving throw at the original DC after two weeks for a  moderate Madness effect last for two weeks and one month for a major Madness effect. However, a successful save does not end the madness effect; it simply decreases the DC of the next save by 1/2 the character's Charisma modifier (rounded up, minimum 1). The madness is not completely cured until the DC is zero. 
There are other things you can do and spells you can cast to decrease the recovery time, but that sounds like a job for a Knowledge check. :)

Prognosis

If a character fails another Madness save while already suffering a Madness effect, they do not gain a new effect; they merely sink further into their insanity, losing 1d6 points from Intelligence, Wisdom, and Charisma.

SEE ALSO: Horror Effects