Well, I've had two skill encounters half-formed in my head, although only one can be applied to multiple situations. It's sort of a double diplomacy skill check, going by the categories you've listed. One thing I will note, however, is that I wont be telling my players anything about required successes or failures, and I wont give anything more than a vague hint of the difficulty of an action. The same action shouldn't be able to be either easy or hard, depending on the player's choice. The difficulty of the attempt should determine the roll's difficulty, and a simply, rp-based warning before a hard action is taken should suffice from a mechanics perspective.
Of Plans and Panics
[The Plan: DC 14; 5 successes/3 failures if presenting their own plan, 4 successes/4 failures is backing another PC]
[The Panic: DC 16; 5 successes/2 failures]
The PCs are holed up in a temporary shelter with a small selection of local townsfolk. The threat outside is still very present, but for the moment, docile, and with an uneasy calm settling over the scene, the townsfolk have begun to fall upon each other. Several men argue over what plan of action they should take; whether or not they should flee and if so, where to. The terrain surrounding the town will likely determine what arguments are likely to be adopted by townsfolk, so no suggestion will be given here.
Meanwhile, the more perturbed of the men and women begin looking out the boarded windows with anxious eyes, their panicked minds settling on plans of action without much conscious thought. The number of these men and women can vary depending on the DM's tastes, but no more than the number of PCs is probably a good rule to go by.
Suggestions: Intimidate, Bluff and Diplomacy are the most obvious ways to present arguments to the more rational survivors, but Knowledge checks can be used to present raw data that favors their position. Perception can also be used to get a firmer grasp of the situation outside, while insight can reveal a bit more about the survivor's mental states. Athletics and Acrobatics are the least likely to come into play, but may actually be found useful if used to somehow impress the townsfolk.
As for the panicked survivors, Perception and Insight will be big ones; these checks, when applied to the planning townsfolk, can also apply a single success to this side of the challenge by revealing their mentally unstable condition. Some may seek to run out and risk their chances alone, while other might destroy what barricades have been set up and fight the enemy head on. Neither situation will help the others left inside, and so Bluff, Diplomacy, Intimidate(which will in most cases be a hard roll, given their already scared disposition) will likely come into play. Heal, and some knowledge checks, may also give insights on how to deal with such mentally unsound people.
Development: The planning argument is likely to sway back and forth, and rely heavily on rp interaction and the arguments adopted by the townsfolk. Successive failures will cause arguing townsfolk to begin to gang up against the PCs, while each success might win an NPC over to their side. NPC sucesses may cancel out PC successes, if you wish you allow it.
On the other side of the event, each failure, regardless of attempted difficulty, will raise the success DCs by 2, while successes will lower it by 1. This is based off the changing mental states of these men and women.
Total Victory: All NPCs will assist the PCs in their suggested plan of action, and everyone is given time to prepare.
Planning Victory: The 5 NPCs involved in the argument all lend the PCs their support, but the panicked townsfolk flee into the night, weakening the building's defenses and bringing the enemies down upon the alliance before they have time to properly prepare.
Panic Victory: The PCs will be on their own once the time comes to leave(or not leave, depending on which NPC you want to have won the planning argument) their shelter, but they are still given time to prepare and gather supplies from the NPCs.
Total Failure: The panicked townsfolk let the enemies into the shelter, and the NPCs scatter to the four winds, leaving the PCs to fight a difficult battle alone, and without time to prepare.
Far Realms Fragment
[DC 14, 6 successes]
This is a very niche challenge... sort of a cross between 'scale the mountain!' and 'avoid the traps!' Basically, in the one-shot I include this in, a living piece of the Far Realms is transported just outside a small town at about the time the PCs arrive. After a short rp event with the town guards, they fight their way to a shelter and do the prior skill challege. They then either fight their way out of town, or towards the Mist's source; this challenge is directly related to the Mist's source.
A mountain of living flesh rises up before the PCs, connected to the earth by a ring of fleshy tendrils around its base which have dug deeply into the ground. Some areas of the living terrain are sheer, slippery cliffs, while in the more gently sloped areas, 'muscles' flex beneath the mountain's flesh, causing the ground itself to buckle and rise in an attempt to buck off any ascending interlopers. The rest of the terrain varies in its rate of ascent, but are bound to one another by the long, writhing tentacles which even now lash down towards the base at the gawking PCs.
The challenge is conducted in 6 'phases' with one success per PC allowing them to move to the next phase. Provide unique terrain features, and differing numbers of tentacles for each terrain to encourage alternate solutions for ascent.
Suggestions: Depends on the 'phase', although for the provided example, Acrobatics will primarily come into play for the 'muscles', although solid jumps from Athletics will work just as well. Athletics will serve as the primary method of ascent at the 'cliffs', while any number of strategies can be used to bypass the tentacles. Knowledge and hard Perceptions checks can reveal crucial, helpful knowledge that can decrease and entire phase's DC or create new ways to ascend(for instance learning that the tentacles rely on rather weak, but long ranged tremorsense to find targets may inspire new ways to bypass them, at a bonus, of course), but will rarely allow for automatic ascent, as there are still physical trials to bypass. Allowing for 'safe paths' for these checks in early phases may work, however I would suggest removing them from later, supposedly harder phases.
Developments: Each round a PC remains stuck in a phase, the DC rises by 1 as the Far Realms Fragment begins actively working to inhibit that slower moving target. On the other hand, allow for self-sacrificing, or team oriented solutions to provide free successes for other players, possibly at the sacrifice of the skill user's success for the round. Yes, that's right, each PC is moving at his or her own pace, although running ahead is not likely to happen due to the dangers of doing so. Those who get ahead can always choose to use skill checks that simply grant successes to those left behind(although the DC in their phase will of course continue to rise).
Example- A Fighter uses Intimidate to physically harass the tentacles, drawing their attention to himself as the rest of the party passes by. You may judge that this puts him at more than a +1 DC for the following round, and his challenge for the phases has changed from 'find a way up' to 'somehow escape from the tentacles'.
Total Success: The PCs reach the summit, and face the 'Heart' of the fragment to remove the aberration, and the Mist, from the face of the earth. (a solo battle I have prepared as the one-shot's finale)
Single Success: That PC advances to the next phase.
Single Failure: That PC takes a small amount of trap damage(5, or preferably less; this is meant to weaken PCs for the start of the next fight, not kill them!) from the violent terrain, and fails to proceed upwards.
Total Failure: For this skill challenge, total failure is theoretically impossible, unless the PCs roll SO bad that they all fall unconscious and die during the challenge... which should hopefully have the same chance of happening as in a very small(half the suggested encounter XP) minion fight. Meaning it'll take some VERY bad rolling from the ENTIRE PARTY over a LONG PERIOD OF TIME to do.
