If you're a GM, how do you portray an NPC who's much smarter than you are?
Does anyone use a method other than through some sort of GM-fiat?

Now, what if it's a PC, though? How can the player successfully portray a supergenius?

If a player is a genius I might give some extra hints to the player. Stuff like "Despite this woman's claim that she is the queen's daughter, you remember the Queen said she had two daughters, and you have met both of them." This ofcourse doesn't mean the woman isn't actually the hidden third queen's daughter, being smart doesn't mean being always right.

Portraying a villain requires skill and effort from the dm so there isn't an easy solution. Ofcourse in certain situations being a genius doesn't change things, so in that case there nothing special needed.

I play every character slightly more stupid than they are.  This means that the characters that are smarter than me can just be played to the full measure of my intelligence, which relatively makes them the smartest NPCs in the game.  I usually rationalize this as various flaws the NPCs have that lead to less than optimal behavior. (This guy is smart enough not to do X, but lacks the will to stop himself.)  As a bonus, it also makes the really stupid characters stand out.  I view this as akin to stage makeup used for a character on film.  

For players, if someone is playing a character that is extremely intelligent (or wise or socially adept or similar mental or emotionally advanced), then I give the player a lot more wiggle room to get help from the rest of the players, even in a crunch.  We have even formalized this in some campaigns:  A high intelligence wizard player has the ability when making a decision to stop the game, ask for a quick discussion by the players, and then pick the suggestion that sounds best to him from all the players, as if he came up with it himself.  The wizard player does still have to make the decision.  This doesn't always lead to the best decision, but it does create the feel that the wizard has considered all the angles.

Edit:  Also, I'm smart enough to be well aware that intelligent people do stupid things all the time.

It depends a bit on what they're a supergenius "in". I tend not to play superhero games, and tend not to have characters whose high intelligence is thought to just mean they're ultra-smart in everything. And I play games with no overall "level" for characters and where attributes, talent/proficiency and skill levels result in concrete ability scores in different things, so the system provides a strong effect automatically.

In general, I expect the GM (whether it's me or not) to take into account the intelligence, knowledge, perception, etc of characters and give them appropriate consideration and advantages compared to characters with less of that. Usually the GM has much more information than any characters do about the world, situation, and what makes sense, and can have NPCs have more appropriate ideas, knowledge, perception, etc. Players can also be given more and better GM tips, up-front smart options, information, suggestions, and be interrupted when doing things the GM feels their character might know better about. Smart characters can also be given fewer opportunities to do unsmart things, and/or clearer more insightful explanations of potentially confusing situations. Also giving the players of smarter characters more real-time to consider their decisions and more leeway in asking the GM what their character's impressions/ideas are about things.

One thought is that many super geniuses don't necessarily have much better common sense than the rest of us, so the super genius may mostly come out in ways that are easy to handle with game mechanics. If they are an inventor for example, player or GM intelligence can come up with the idea, but game mechanics can be used to adjudicate how long it takes to make the invention and how successful the invention is.

Frank

I play them Sherlock Holmes-y: they notice little details and draw (correct) conclusions from them; things that wouldn't normally be evident. Sometimes I make up the details as I go along, even if they haven't been previously specified (i.e. they aren't things the dumber PC would even think to notice).

Examples: "The still-damp mud on your boots shimmers with the slight sparkle of blue mica, indicating that you've most likely recently visited the one lake in the vicinity around which that mica exists," or "the butter stains on the edge of your spell component pouch clearly indicate you favor a Grease spell."

Quote from: Zalman;1031853I play them Sherlock Holmes-y: they notice little details and draw (correct) conclusions from them; things that wouldn't normally be evident. Sometimes I make up the details as I go along, even if they haven't been previously specified (i.e. they aren't things the dumber PC would even think to notice).

Examples: "The still-damp mud on your boots shimmers with the slight sparkle of blue mica, indicating that you've most likely recently visited the one lake in the vicinity around which that mica exists," or "the butter stains on the edge of your spell component pouch clearly indicate you favor a Grease spell."

Holmes is my go-to model, too. I think of supergeniuses thusly:

Q: How do you keep a supergenius from uncovering or deducing matters you want kept secret?
A: Keep their attention focused elsewhere.

(See the BBC's Sherlock for an example of this in action, particularly how Mycroft handles Sherlock during the first three seasons. And watch season 4 for what happens when Mycroft gets outmaneuvered on this very score - and not by Sherlock.)

I just act normally.  

Use big words and claim to have known things were going to happen after the fact just like any self conscious nerd.

Quote from: RPGPundit;1031819If you're a GM, how do you portray an NPC who's much smarter than you are?
Does anyone use a method other than through some sort of GM-fiat?

Now, what if it's a PC, though? How can the player successfully portray a supergenius?

I'm playing one in Traveller (EDU=F, maximum human ability). The system gives you additional abilities if you get such a character, like being able to look at a situation and instantly spot the small details, or to make difficult calculations in his mind:).
On top of that he can master whole branches of science in weeks, to a professional level, just because of how the system's modifiers work.
Nobody in his or her sane mind questions his abilities, so I'd say it's successful;).

Decide what areas they are a genius in.

Decide at a high level what general stratagems they employ in the areas they care about.

If PCs decide to do something that would interface with these stratagems, give the supergenius wide latitude as makes the most sense according to its motivations.

They pass INT checks a lot more. I also assume greater mental competence, so they get freebie INT checks via GM provided insights.

When I play a high INT PC, I will usually ask "would my PC know XYZ?" and that usually results in freebies or easy to hit INT checks.

Depends on the setting and what the genius is a genius at.

Could be they are really good at crafting magic items. Or just really good at crafting period. Or they might be an incredible architect whos structures are far more sturdy and can take a pounding longer. Or they are like the sages from AD&D who might have encyclopedic knowledge on some subject like herbs, potions, languages, cyphers, whatever.

As for a PC. Depends also on the system and what really the PC is good at. What are their areas of super competency? What areas are they deficit? Set some limits and stick to it.

One thing to use really sparingly is the conceit that makes slasher movie villains apparent geniuses: the are omniscient and are always in the right spot for the characters' actions or have thought of whatever the player just came up with. Whatever the PCs do to out-think the big-bad are inherently thwarted because the DM decides retroactively that the big-bad would have a counter.

On the other hand, it is pretty reasonable to think through and say to oneself (as the DM) 'what information gathering measures would the big-bad have in place, such that they would have advance warning of some plan like this?'

That is because the least realistic supergenius is a (successful) version of The Princess Bride's Vizzini (Vizzini, however, is a great example of 'falsely thinks they are a genius'). You do not just see a man in black and think your powers of observation and tactics are going to make you win the day. A real genius would be one who has reconned the entire situation, figured out what potential actors are in play, what situations might come up, etc., and have the correct forces in place to prevent the impasse Vizzini found himself in to happen in the first place. Real (especially tactical) genius is a matter of information and logistics.

If it's a supers game then I cheat mercilessly. If it's a high INT character in a fantasy or sci-fi game then I like to give them plans within plans and at least 12 of those are contingencies.