I am having trouble finding a good system for a mentally impaired friend of mine. I have a player who does not want to form emotional attachments to characters (or anything else in the game fiction) and also hates making decisions. The player also cannot learn anything but the simplest of rules without effort beyond that which we consider reasonable, and has a very short attention span.
The player enjoys writing, and is interested primarily in the collaborative storytelling aspect of RPGs. While she doesn't care about the characters or societies or overall fiction on an empathic level, she enjoys having specific outcomes happen and pursues causing these things. I do not know how she comes up with what she wants to have happen, and it changes frequently regardless of whether or not she is successful. The most common ones seem to be "Make horrible things happen to my character, generally in a physically brutal way. ((I don't want to die though, and I don't realize that the actions I'm taking are very likely result in death and/or permanent disability))", "have my character be useful for X thing another PC is trying to do", and "Be as evil as possible, just cause. Retroactively change what I do to make it worse repeatedly as I struggle with the idea of evil and come up with new and exciting ways to do horrible things", and "be accepted by society and liked by everybody". Moving between these, which happens about once every thirty minutes or so, often causes her to be upset because her previous actions inhibit her new ones or cause her to think the rest of the players are punishing her (see point 5 of the next section). For example, she once realized that graphic descriptions of human mutilation were gross so she repeatedly sought out ways for her character to get other things to mutilate her, and then tried to describe in graphic detail, and have me follow suit, exactly how the creature's teeth ripped her open and her entrails split apart, etc., but (after we had some discussion about character death) was confused and upset when later she was unable to help one of the party members go running (by going running with them) because she was in the hospital recovering. The things she wants to happen are not always macabre, but various kinds of pain inflicted on various subjects in different ways does seem to come up at least once a campaign (not once a session), though this may be tied to getting overwhelmed with things.
The player enjoys the collaborative world-building aspect of game-prep in FATE and Dawn of Worlds.
The player is often too self conscious about her mental disabilities to engage with the game, so I do not know the full extent of what she wants in an RPG. She is also unwilling to talk about this, other than declaring that she likes them and occasionally requesting to play City of Flowers (an RPG system I made a while ago, the campaign she played in which she seems to enjoy talking about whenever she isn't playing it).
Most inquiries are responded to by her hiding behind someone/something and making angry animal noises.
This player is very easily overwhelmed. When the player is overwhelmed by an emergent situation in the game the first few times in a session I think, for various reasons, that it would be beneficial both to her RPGing experience and to that of the other players' if the situation could be abandoned in keeping with her very strong inclinations in that matter. The player in question would be happy with completely abandoning any campaign as soon as an overwhelming situation came up, but this is too frustrating for the rest of the group to handle.
Fate 2.0's character creation time (with the rules already understood) (~1 hour max) is pretty much the absolute maximum time we can spend doing prep-work involving the player for a system to be feasible. Shorter is better. No prep-time is the best.
It's ok if she has to know some rules, like how to roll dice if there's only one consistent method, but the fewer rules she needs to understand the better. Dice rolling is not something the player enjoys. We have taught the player a simplified version of the rules to make characters in FATE 2.0, but it was a long and arduous process for everyone involved (though probably worth it). When we actually play FATE, though, other players help her check off aspects and spend Fate points and decide what to do with those things in order to accomplish the stuff she wants to accomplish in game. This is sometimes difficult. The easier it is for people to be able to deal with any abstract meta-game things for her the better.
She often refuses to articulate reasons for refusing other player's ideas when she doesn't like something and just says "No" in an artificially childish voice repeatedly. This is her response to not being able to engage in rhetoric capable of convincing people of things. Having some way of letting her do this a little bit, so she doesn't feel trodden upon, while limiting how often she can do it so she doesn't trod over others, would be good.
It's not a problem if there are some in-game consequences to things but if something she doesn't like happens as a result of her actions and it keeps coming up, she feels like we're punishing her for being dumb, which isn't good. We have talked about this and she understands that no one is trying to do this, but she still feels this way when this happens and so minimizing the recurring reminder factor for decisions that are perceived as 'mistakes' would be good.
She doesn't like it when rules pertaining to her character are in other peoples' hands because she feels it impinges her agency. She doesn't like learning rules, but she's willing to do so if it would help with this and doing so is reasonable. Abstract or complex rules are extremely difficult for her to learn. Rolling d20s in D&D 3.5 is a good example of something that it would be practically impossible for her to learn; there are just too many edge case things that affect what rolling a d20 means. It could be attribute bonus + d20. It could be some skill ranks + attribute bonus + d20. It could be saving throw + d20 or Base save + attribute modifier + d20 or maybe those are the same sometimes. It could be the bonus from standing on high ground + the bonus for a masterwork longsword - the penalty for being shaken + BAB + STR (or DEX, since you have Weapon Finesse) + (did you want to Smite Evil now or later?). This is not good. Extreme rule parsimony is desired.
One of the primary things that overwhelms this player is having too many options and thus feeling unable to choose any for fear of choosing the 'wrong' one. Limited choices helps the player interact with the game more frequently, but runs the risk of frustrating her if she can't do something she wants to do because of rules that she doesn't understand. 'Intuitive' rules would be better, but her intuitions are often radically different than other people's in ways that are unhelpful to her so many things that seem 'intuitive' to able-minded people will not to her.
Having to make decisions is the other (and greater) primary thing that overwhelms the player. It's not that she never makes descisions, nor that she doesn't want to make decisions. She just can't have to make a descision-- no matter how small or obvious-- or she freezes up, freaks out, and gets unreasonably upset with everyone. This is a problem with character- focused RPGs because we can only ignore her character for so long before we really need to know whether she is, for example, leaving the ship with Jane or staying with Bob. I have been using various GM-techniques to get around this for a while but it is a royal pain and I'd really like the system to just take care of that for me. This is one of the primary reasons I am considering Microscope; I think she will be able to join in when she wants to and just watch and not make any decisions when she wants to without the game 'forcing' her to make a decision. I want explanation as to what that would look like and how that would work.
She doesn't care about her characters except in a very non-empathic way. This is why, for example, Polaris wont work for her. She doesn't care about her character or other people's characters as people, she cares about them as toys. Not like 'it's a doll, lets have a tea party' toys, like 'it's a doll lets burn it and see what happens'. If the game is designed primarily around players deriving value from qualia resultant from empathy with some aspect of the game fiction, this will not work. Some minor amount of requisite empathy is ok, but it can't be about in-character emotions/drama because there won't be any.
She pretty much can't do math. Maybe some extremely simple arithmetic (adding and subtracting) would be ok, but multiplication is right out, as are fractions, decimals, differential calculus, etc.
She has trouble separating 'Bob's peace and art loving elven aristocrats don't like my murderous, foul-smelling, goblin raiders' and 'Bob doesn't like me and thinks I smell bad'. We deal with this regularly by stopping the game and having conversations. The less time we have to spend doing this the better.
I've dealt with GMing for mentally impaired people before, with differing kinds and severities of impairment. I'm looking for a good system for this person in specific, not 'mentally impaired people in general' and doubt that such a system could exist with any quality. The desires of myself and the other players need not be of concern.