A character has a certain alignment that in general defines how he acts. With multiple personality disorder or other similar disorders (maybe bipolar disorder with severe depression/severe mania), there may be a dramatic change in how one acts and thinks.
First, would a change of personality alter one's alignment?
Second, are there any tips on how to accurately and realistically role-play a character with one of these disorders?
Just assign the character the chaotic neutral alignment. If it helps the players or GM, you can privately assign personalities separate alignments, but their character effectively is still CN.
This might vary by edition, but Pathfinder includes this suggestion:
Actually, it sounds like fun for a LG personality to be confused when their good-aligned equipment doesn't work for them...
There are no explicit mechanics for switching personalties. Come up with your own or work it out while roleplaying.
Working out with the player what dominant personalities are in the character and what their 'triggers' are will be helpful. You'll want to be careful about personalities with dramatic changes in alignment on characters whose class require certain alignments. If a multiple personality character shifts from Lawful Good the GM will need to decide how that works. Does the player lose their Paladin status if they shift to Chaotic Neutral? Will it come back when the right personality shifts back? Ultimately the GM will probably need to decide how to handle this.
Here's some tips and advice on trying to implement this.
As previously indicated, determining which personality comes forth needs to be worked out. Are they random? Do they have certain triggers to invoke them? Discuss your intent of roleplaying the disorder with the rest of the party out-of-character. If any of the personalities are particularly hostile or violent towards the other characters, the group should have a little prior warning to prevent a game from turning sour.
In terms of mechanics, certain personalities may favor different weapons or prefer to use certain skills/spells over others. A multiclass character may help add emphasis to the multiple personalities to give you more abilities to work with. Rather than trying to create new/homebrew rules to support the disorder, try limiting parts of your character to specific personalities under the existing guidelines.
One of my characters in an online game has a second personality. The personalities talk amongst themselves. Her character speaks in the main chat channel of the game, while another player represents her second personality and speaks to her privately. This has made for some interesting reactions from my party as they get one half of a conversation...
In a lot of ways it really depends on the cause and type of schism that is being made. I would venture that if the personalities vary in behavior and motivations substantially, each personality would have its own alignment and would operate as that alignment as long as that personality is dominant (If the personalities are a Quorum style, the lead personalities alignment would play through).
The biggest concern would be players using it to their advantage instead of the debilitation it truly is. I suppose a wizard could schism their brain to process different things better, again depends on the nature of the state.
Often the cause of the schism is related to its triggers, if it is PTSD related then times of stress will cause loss of personality control, or a personality switch. If it is magical, the rules are in the eye of the caster.
Although most of this is related to MPD, much is true for bipolar etc. One idea is to set trigger points (overcast sky, stressful situation, being separated from your security object) requires a will check to remain in control.
IMO the biggest thing is to treat it with the respect it deserves, all to often in RPGs we use mental illness as an excuse to be goofy or to do weird things, but remember to your character it is a serious, frustrating condition. Many people with such illnesses describe it as being trapped in their own bodies. Again use of randomness like willpower checks (with compounding difficulty based on situation), and such things can help allow the player to "get in the head" of one in such a condition. Just don't make it so frustrating it is no longer fun. There is a reason why WoD says such conditions are for "advanced players only"!
Good luck!
Terminology: Bipolar disorder, depression and mania can give big changes in personality, but they are mood disorders, while exhibiting multiple personalities (actually a symptom exhibited by more than one possible underlying condition) is not. Switching personality is a symptom associated with "aberrant perceptual experiences and disruptions in reality testing" (Yogaratnam and Jacob 2012), which are not mood disorders and arise from conditions such as schizophrenia and dissociative identity disorder. Both mood disorders and these conditions that warp ones link to reality can be destructive, sometimes they can coexist, but they are very different beasts. Having a switch between personalities that have different religions would not be a mood disorder, I think.
Yes, you should definitely allow identity-switching disorders, not to do so limits your game needlessly. Some possible ways of handling alignment issues and relationships to the divine:
Don't try to mechanize this: this is not the realm of conflict resolution but of roleplaying.
I played two such characters, one in DnD-3.5e, and the other in DnD-4e.
The first was a human Swordsage, that used maneuvers and stances from the Desert Wind and the Shadow Hand schools. When he was in his "manic" state, he used only Desert Wind maneuvers, and he was flamboyant, happy, social and even foolhardy. When he was in his "depressive" state, he used Shadow Hand maneuvers, and was sneaky, reserved, taciturn and very cautious. The switch in personality came depending on the situation, but some strong emotion (anger, fear, lust) made him change personality instantaneously. My DM didn't like the character because it was a little unpredictable, but it was very fun to play.
The second was a genasi Swordmage, that had the Firesoul and Airsoul manifestations. The personalities were similar to the first character, and he used only elemental powers with the fire or ice keywords depending on the current manifestation. The switching was also similar, but he could switch personalities (and powers) during combat for the duration of the combat. When he reached paragon tier, he could go Stormsoul when using an action point...and that was his "real" personality, but emerged rarely. I planned to develop it further and by epic he'd be more Stormsoul that the other manifestations, but our campaign stopped. I was both DM and player, and while it was difficult to play a double character and be a DM, it was very funny and entertaining nonetheless.
The point is that if you can make the character fit in the game world, and if you don't abuse the mechanics, you can even bend the rules and have a great game experience. The alignment is not a problem in 4e, but in 3.0e and 3.5e could be, and it makes for even greater fun to switch whole classes (not only powers). If your DM agrees to bend the rules slightly, you will have a lot more fun, with a little more roleplaying effort.
I dont think real world disorders as they really are belong in D&D, but that doesn't mean the game is without forms of insanity based on old school rules. Alignment also plays a role here (more below).
With multiple personalities, if the curse allows for a distinct personality (ie has its own level, skills, etc), then experience is going to be divided up between personalities; if it doesn't explicitly allow for a distinct personality, then they share all the skills/levels of the 'host' and have the same alignment. Shared values doesn't mean the same thing as same personality after all.
If you hold alignments are the true world view of the character, then Id say a number of characters would be insane by virtue of holding that alignment. Someone who is truly CE/NE/CN who have fully integrated their world view into their personality and day to day actions could be considered bonkers.
How Ive handled insane characters (ones that show multiple personalities or by nature of modules saying they are cuckoo, but not "Confused") in high fantasy Forgotten Realms is by world view. For example, many wizards in FR have been referred to as "insane", mostly for holding particularly weird or diabolical beliefs. That can be handled with alignment - also, there really isn't a cure for this - its just the way they are.
I'd treat this exactly how you would treat a cursed, intelligent sword (or similar items / spells) taking over a player's will.
The "cursed" personality of the character can be played by the same player or by the DM (or DM can "overrule" some aspects...).
Triggers to swap between the various personalities could be the most varied: day/night, injuries (for example a character can be very courageous and daring until he suffers the first injury, then turns to be a desperate coward...), seeing a particular animal or situation that triggers a phobia, seasons, particular results of dices... With two different personalities taking over in turn the same body, different alignments can be fully acceptable.
It must however be fully clear to the player which personality is "master" at any particular moment and the player has to role play accordingly, otherwise the DM will have to "take over". This is supposed to add fun and flavour, not to allow breaking rules for an advantage.
I would set it up with your D20 to make it fair... like lets say whenever you roll a 1 you switch persona's it would be cool to have a stealthy char that avoided conflict & then swapped into a in your face attacker.
