For simplicity purposes, assume we're using spontanous caster varaints for spellcasters and spellpoint system..
*PC*
PC believe themselves to be the original clan. That all other clans descend from them, and have commited great heresy which is why they were expelled and formed their own arrogant, sinful paths that delay others from seeking the truth and salvation..
PCs are definitely the most religious of the clans, as well as the most non-negotiable. They are very strict and quickly will "ban a member from their server". That is to say expell them from their organization. The clan is composed of many sects, divided, but they all answer to the same vatican-like authority.
PC Classes: Any divine spellcasting class.
PC class flaw: All PC magic has "lag". PC members are taught to rise above the lag and learn patience and precision. Besides the spellpoint cost, a spell takes a number of extra rounds to cast equal to the spell's level. So cantrips have no extra waiting time, where as level 9 spells take almost a full minute to wait for the spell! And in the hectic battles ahead of you, a minute can be a very long time!
*NINTENDO*
The clan nearly as old as PC. Nintendo tend to be distrusting, and though are not as strict as PC, are loathe to trust anyone, even eachother! They have a plethora of secret handshakes, plays on words, and other means of keeping themselves under a low profile. (Kind of like how Wii requires a code to add them to multiplayer)
Nintendo Classes: Any arcane class:
Nintendo class flaw: Spells have a percentile chance of failing whenever they are cast. When you're deal damage, you roll a d100 and try to roll equal to or greater then your current amount of damaged HP. If you fail, so does the spell. Think of this as Nintendo casters rely more on gestures for their spells. Somatic/Verbal/Concentration. Because of this, a large ass-kicking to the body makes this increddibly hard to perform adequitely...
*SONY*
Sony actually appealed to the common folk. When PC was once the only game in town, and then quickly Nintendo got on the scene and was just as bad. A sortof communist kind of revolution took place of the working classes where they roseup against their magical oppressors. Sony tries desperately not to be like the other clans, and spends the most time devoting time and resources to converting new members. This however makes them kind of aloof and ambivalant to members currently onboard. They're kind of disorganized and there's rumors that they will soon fall.. Though this is mostly by enemies. Probably just wishful thinking...
Sony Classes: Any non-caster class.
Sony weakness: ...Any non-caster class. lol, no spells/games!
*MICROSOFT*
Microsoft just seemed to burst onto the scene out of nowhere, and it made others very skeptical. Come to find out, their suspicions were correct. Microsoft had been tapping into dark and horrific elements to gain thei power, offering an alternative to the rigid holy authority of PC, the disciplined meditative structure of Nintendo, and the collectivist drivvle of Sony. What the they didn't know (atleast noone but the higherups) was that all this abuse of dark matter unleashed something epic... something evil...
Microsoft Classes: Any psionic.
Microsoft weaknesses: Whenever a power is manifested, there is a 5% chance of summoning "The RROD" (The Red Ring of Death) a foul demon from the elemental plane of fire (overheating) that exists only to consume others. It's hostile only to the idiot who summoned it, or any who try to get in it's way of destroying them.
I immagine the PCs would either be a part of some sortof peace treaty doing missions involving trying to earn trust between the clans so they'll atleast stop attacking one another, all be expelled from their respective clans and form a resistance movement, or are loyal clan members and are on neutral territory. Or maybe some combonation of the three.
Hell, I could have them all stranded on an unknown planet and have to rely on eachother for survival and hope they can survive untill they can communicate back to their respective clan for help.