Crime was always with us, he reasoned, and therefore, if you were going to have crime, it at least should be organized crime.
—Guards! Guards!, by Terry Pratchett

For the Mastermind, adventuring is just another kind of extralegal diversion. The same lessons and talents are useful: Have a Plan. When the Plan fails, have Another Plan. (In fact, it’s pretty much plans all the way down.) The Mastermind is one of the most respectable criminals you’ll ever meet: she places great store by intellectual pursuits, and appreciates the finer things in life, as so many thieves don’t. The Mastermind cannot perform some of the amazing feats of the Thief or the Assassin, but elevates the talents of those who accept her guidance.

He [Moriarty] is the Napoleon of crime, Watson. He is the organizer of half that is evil and nearly all that is undetected in this great city.  He is a genius, a philosopher, an abstract thinker.  He has a brain of the first order.
—The Final Problem, Arthur Conan-Doyle

Quick Study

Starting at 3rd level, gain proficiency in one of the following skills: Arcana, History, Medicine, Nature, Religion, Survival, any one tool set, or any one language. You can replace this skill proficiency, tool set, or language with another from this list with seven days of study. If you apply an Expertise bonus to this skill, your Expertise bonus changes to the new skill whenever you change your Quick Study.

Instructor

Also starting at 3rd level, you can teach others to use the same skills that you have honed, though the lessons won’t stick with them for long. Once per short or long rest, you can spend ten minutes coaching your allies to give them the following Lessons.

• Expertise in a skill or tool for which you have Expertise and the target has proficiency
• Proficiency in a skill or tool for which you have Proficiency and the target does not
• Cunning Action: Dash, Disengage, or Hide (chosen by the recipient at time of use)
• Sneak Attack, up to half of your Sneak Attack dice (This does not stack with existing Sneak Attack dice.)
  • Edit: Changed this to +1d6 Sneak Attack die, and no more. Still does not stack with existing Sneak Attack dice.
• Proficiency in Dexterity or Intelligence saving throws
• Any knowledge associated with your Background (This does not grant proficiency, but might allow someone to masquerade effectively as a member of that Background.)
• Temporary hit points equal to 1d8 + your Rogue level

You can give a number of Lessons equal to your Intelligence bonus, and no student can receive more than one Lesson (if offered two Lessons, the student chooses which to heed). The Lesson lasts for 10 minutes. The recipient can decide to use the Lesson at any time before taking a long rest.

Note: This ability will be a lot cooler in actual play if the Mastermind, you know, puts some roleplaying into distributing these abilities. Honestly, though, as long as everyone is engaged in the conversation and has something to contribute, extensive planning sequences can be immensely fun.

The Mastermind’s Library

At 9th level, when performing research (such as through the Researching downtime activity), you gain advantage on all ability checks. Furthermore, one Quick Study option now becomes a permanently-known skill proficiency, tool proficiency, or language. The Mastermind gains proficiency in another skill, tool, or language that can be replaced with seven days of study.

Improved Instructor

Starting at 13th level, you can give out a number of Lessons equal to twice your Intelligence bonus, and no student can receive more than two Lessons. You also gain the following Lesson options.

• Uncanny Dodge
• Evasion
• Reliable Talent
• Edit: The basic Sneak Attack Lesson increases to +2d6 at this level.

The Grand Reversal

Your schemes are wheels within wheels, and you can turn the tables on anyone. Once per long rest, when one of the following occurs to you or an ally, you can use your reaction in the following ways:

• Death (by massive damage or magical Death effect): the dead character is revealed to be alive and well, prone, and at 50% health. If the magical Death effect allows saving throws, the character suffers the effects of failing all but the final saving throw, but does not have to make further saving throws.
• Unconsciousness from hit point loss: the unconscious character is revealed to be merely wounded (healed to 50% of maximum hit points) and prone, typically ripping open a shirt or pulling aside a cloak to reveal an extra-thick piece of armor that is ruined but not pierced. The character can make a melee or cantrip attack against an enemy within range, with advantage, as part of your reaction.
• Charmed: the charmed character was feigning, and can continue to do so (using Charisma (Deception) checks if necessary). At any point in the next hour, the first attack that the character makes against the source of the charm converts a miss to a hit, or a hit to a critical hit, or a successful saving throw by the source of the charm into a failed saving throw.
• Running on Empty: When an ally runs out of spell slots that return with a long rest (including slots that return with “a short rest or a long rest”), the next time she would roll damage for a cantrip, it deals damage as a critical hit (even if it cannot normally critically hit).

Design Notes

There’s a very good chance that Instructor granting even half of the Rogue’s Sneak Attack dice is much too powerful. I originally allowed Lessons to work for just one die roll (and Improved Instructor extended that duration), but I came to the conclusion that that was being too stingy. After all, the other archetypes’ abilities are always-on. (Also, ranged characters won’t get nearly the same mileage out of it that melee characters would, unless they’re purpose-built to do so.)

Granting other characters Cunning Action is really good, but probably less so than it seems at first blush. Cunning Action is one of the strongest uses of a bonus action, especially because it’s always available, but other classes do have things they want and need to be doing with their bonus actions, so I think this might work out all right. Likewise for Uncanny Dodge and spending a reaction, though Uncanny Dodge really is one of the strongest reaction options out there.

The Grand Reversal is the kind of ability that some people love, because they’re okay with embracing gamism and narrativism, and others hate for reasons of simulationism or dissociated mechanics. If you’re in the latter category, that’s fine – this archetype isn’t for your table. Retroactive planning is a big part of how you make heist-like plots work in dice-driven game environment.

This class, called the Thief in 2e and prior and the Rogue thereafter, has always centered on themes of selfishness. This is something of a default roleplaying assumption for Thieves, and a huge number of groups had Thieves that stole from party members. (Also, fucking kender, man. We can all breathe a sigh of relief that they are not in the Player’s Handbook.)

The theme of selfishness is at something of a low ebb in 3.x, and it takes an unusual form in 4e. Famously, 4e is a game that either “encourages” or “outright demands” teamwork, and the word you choose there is pretty much the shibboleth for whether or not you liked the edition. The 4e rogue, then, still fits within the teamwork frame, but does so by capitalizing on the opportunities that other people set up, while generally not offering as much back for other characters to use. More than any other class, the rogue needs combat advantage all of the time – if the rogue has to set up his own combat advantage, you can be sure that some damage potential is going to waste. Thematically, I think this is a piece of understated brilliance, and all the more so because the rogue does have other options.

The point of the Mastermind, then, is to invert that and see what happens when the rogue is the “generous” one. (Notable example case: LotRO’s Burglar class is a master of setups for other team members to abuse.) I’ve seen tons of rogues be the one to make a plan fall apart with a moment of excessive greed – and really, it’s how rogues behave in sword & sorcery fiction, so I don’t blame them. (As I have never been involved in real-life burglary, I shy away from commenting on how real-life thieves behave.) The Mastermind, though, wants to see the heist go off without a hitch, because she wants to prove that she can beat the Steranko Security System.

Also? Rogues are advised to make Int their second-highest score. Is Investigation really enough better than Perception and Insight that this is the right answer? With the Mastermind, it is.