Being that I have a healthy phobia of using other peoples adventure and campaign material, published or not, I find myself constantly working on new encounters and skill challenges. (Hey I gotta fill those down hours at work between 8 and 5) Over the course of creating skill challenges and seeing some others that have been created I have decided to boldly try and classify a good number of different skill challenge mechanics and their purpose or explanation in the storyline.
Now already I have a feeling I've bit off more than I am willing to proverbially chew. I think first and foremost it's best to identify some of the different structures that make up various skill challenge. Since skill challenges are really only limited by the creators imagination there are a limitless number of possibilities. However, just like computer programming there are a number of design patterns that are used over and over again in skill challenges and seem to be very successful. The key is pointing out what these design patterns are and what they are used to accomplish. So here are a few different design patterns I've noticed.
The Trailblazing SC:
Just like the DMing style of trailblazing this kind of skill challenge limits the players choices to only a couple of skills and to quickly lead them along the storyline. Since the story is usually already planned out players will only have 1 or 2 different skills to choose from. In most cases I have seen this kind of skill challenge used to quickly advance the storyline or play a narrative with dice rolls. They require only minimal input from the PCs such as, 'Do you want to go through the mountains or the forest to get to the next town?' Usually these are low complexity challenges because high complexity challenges tend to feel like you're just rolling dice. Basically this kind of SC is used as a narrative or sometimes just introduces an extra encounter into what in previous editions might have just been a flash point or 'Okay a week later you show up in town'. While theses aren't really bad I find them a little unnecessary, the PCs are adventurers if it's not an adventure to do something it doesn't really need to be a skill challenge, then again XP is XP so bring on the trailblazing skill challenges :)
The Resource Pool SC:
The Resource Pool skill challenge is probably the most typical of all skill challenges. This is essentially the framework intended to be used with all (or most all, see social skill challenges) skill challenges. The basic concept is that the party has a pool of available skills to choose from in order to complete the skill challenge. Generally each skill will have some kind of additional effect on top of a success or failure. Such as a +2 to your next skill check or perhaps on a failure, you lose a healing surge. At it's core, this kind of skill challenge encompasses a lot of possibilities for the party. When a group of players are involved in a challenge it makes sense that everyone can take a turn, choose a skill that best suits them and roll to see how they fair. Each individual success or failure brings the entire party one step towards completing the skill challenge.
Since there is a plethora of different kinds of resource pool skill challenges the length of these kind of skill challenges can vary from complexity 1 to complexity 5. More advanced resource pool type skill challenges exist where, based on what skills have been attempted with success or failure, new secondary skills become available that previously were not. A perfect example of this can be found in Dungeon 167 in the"Heart of the Forbidden Forge" adventure in encounter 14: "Disabling the Forge" just to point one out at random.(requires DNDI subscription) It should also be mentioned that in some cases not all available choices in these kind of skill challenges are made known to the players, thus forcing them to come up with their own ideas about how to complete the challenge. In other cases resource pool skill challenges can be modified to become Diminishing Resource Pool skill challenges which add an extra level of decision making on the part of the PCs.
The Diminishing Resource Pool(DRP) SC:
The DRP skill challenge is similar to the resource pool skill challenge but rather than allowing the players to choose whatever available skill they want they are limited to successfully completing each skill a limited number of times. Sometimes a skill will only be good for one success other times the player may be limited to a small number of successes. Sometimes on a success or failure one skill will be replaced with a different skill in the next round. All of these variations build on top of the original idea of the resource pool skill challenge and add the element that certain skills' effectiness deminish as they are used.
When the players have to choose which skill they will attempt on their turn they need to look at who is the most skilled in the party rather than just what their character's best skills are. The idea being that once a skill is used the group might not get a chance to use it again potentially forcing players to make skill checks with untrained skills. This kind of alteration can throw some PCs off their guard, especially when they don't know they are doing a DRP type of skill challenge in the first place. This kind of logic closely follow a lot of fantasy world situations and can make for great enthralling chllaneges. The only downside I have seen among them is that they are usually pretty involved and take a good deal to time to create and flesh out.
An example of a DRP SC might be where the PCs are trying to crack a cipher code on a magical scroll. Each piece of the code can be broken in a unique way but once solved there is no new information that method can present. Say initially the PCs can use insight to learn about the origin of the scroll or Arcana to decipher the magic encrypting it. Succeeding in insight tells the players it has a religious origin opening up a religion check where as the Arcana route displays the text in a certain dialect allowing the players to use nature to determine information about the writer. If the players then succeed in a nature check perhaps they learn it was written by an ancient tribe of magic wielding orcs which could warrant a history check or another arcana check. With each player taking a turn in this kind of challenge the party needs to make sure that the dumb barbarian doesn't end up getting stuck having to make the history check to which he knows nothing about.
The Group SC:
The group skill challenge is a challenge in which the entire party makes rolls as a group. When I say group I mean literally just that, every one's roll weighs in on each others chance of success. Generally this is done with the majority of the party's rolls needing to be successful in order to count as a success towards the skill challenge. If the majority of the rolls are unsuccessful then the party earns a failure towards the encounter. This kind of skill challenge works great for adventures where the entire party is trying to accomplish a similar task such as scaling a mountain or trying gain control of an of crashing air ship. Group skill challenges tend to have a few different skills to choose from and often require at least 1 player to use each of the available skills. As with pretty much all skill challenges variations can exist where the set of skills change. This kind of change tends to have more of an impact with group challenges if a certain number of PCs need to make checks for the new skill presented. A lot of the time such a change can lead to characters making checks for skills in which they aren't trained which can make things tougher, but usually more exciting.
The Puzzle SC:
The puzzle skill challenge as it's name suggests involves an actual puzzle set inside the framework of a skill challenge. Depending on the difficulty of the puzzle this can sometimes be extremely easy or very difficult. Generally this type of skill challenge will deviate from the typical x successes before 3 failues and instead uses some sort of time limit. This arbitrary limit is the amount of time the players have to work on the puzzle. These kind of challenges really give the player's a chance to get their hands dirty, however for those not fond of puzzles it can come as a distraction from the game. Some player's may also not like it when the half-orc warden who has never seen a book in his life and is dumb as bricks is able to solve the riddle the Sphinx while his worldly wizard ally is dumb-founded by it. This can be a draw back because much of the challenge of the puzzle relies on the player rather than the player's character.
To help supplement what a player's character knows there should be skill checks that are made during a set interval of time. Each successful skill check made gives the players a piece of the puzzle that they haven't already solved. A very clever example of this I came across in another DMs game was when the DM wrote out symbols in 'elven' on a grid as glowing runes on a locked door. It quickly became obvious the grid was a sudoku puzzle using symbols rather than numbers. The runes started glowing brighter as the players interacted with them hinting that something very bad would happen if the puzzle wasn't solved quickly. Suddenly the group of players realized the DM was timing them and everyone scrambled into action trying to solve the puzzle. Every few minutes a player could make a certain skill check to solve an empty square. In this case it was exceedingly simple and easy to implement but it got the players involved as if they had just stumbled upon an angry dragon. However, while puzzle skill challenges can be very entertaining you want to make sure to use them sparingly. Too many and your player's will stab you in the throat with a pencil when you're not looking because they came to play D&D not solve puzzles.
While this post turned out to view skill challenges at a much higher level than I anticipated I believe these 5 patterns do a pretty good job of classifying many of the skill challenges out there and many more to potentially to come. I purposely didn't launch into any detail about social skill challenges since I already have a post on them, granted it's not quite the same thing but no point in reiterating the topic. For those of you who are still actually reading this far you probably want your 5 minutes back that I just wasted but I'll make it worth your while and say if you want to read some more about skill challenge design you can check out Mike Mearls' articles on skill challenges, they are very enlightening.