Anyone up for suggesting a setting or scenario? I'll go from there to add mechanics and encounters.
For my own part:
I. A more lore-driven dungeon.II. An exploratory dungeon.Phantom Train, but it's the real deal instead of a recreation. Let's say it... conveys souls between shards, but with an emphasis on shards that have collapsed and been rejoined or are soon to do the same. (Yes, it hints at incoming futures, though said futures are of course mutable.) Your objective is to swap to the intended line. Think of it's opening like that of Westworld mixed with the train scene of Spirited Away. It is by no means a traditional dungeon.
Most souls on the train can be interacted with, gleaning lore hints. In the initial, story-based run, the dungeon is run largely via a multi-step quest rather than simply sprinting to the end, with non-skippable (though speed-able) conversations and so forth, with much of the feel of exploring Amaraut. The souls assume you are like them: you await the end, and are --if in some reluctant way-- happy to be conveyed to it. These souls are in some way like you, "warriors of light", though some have retained their memories between rebirths and others have retained only fragments between reincarnations or being hosted anew (waking up, the next day, having been a fisherman all their lives, who had merely dreamed once of having been a cavalry scout); each alike has grown weary. The story-run proceeds by trying to figure out how to escape, essentially hijacking the train so that you can again reach your intended world. There are, per usual, boss fights, but the rest is predominantly investigation, with a surprising amount of side-content coming in handy. Apart from a few central bits, the pertinent clues gleaned and their relevant mechanics change per run; you cannot merely learn the run to devalue investigation.
In the hard mode, however, all the machinery of death here, so to speak, knows that you've committed taboo and will attempt to stop you. Rather than subtly wrong, the world seen outside the train is obviously shattered. Flooded, with broken floating earth in the distance and water pouring down, up, left, and right. Looking down, one can peer through the water into a mirror world. The previously passive mobs and the train's staff will now fight you, and they are difficult af. That said, the dungeon has a unique pathing or mob-skip / fight-selection mechanic. You can fight in, atop, or on the sides of the train, and pass through to the mirror world by walking down the side of the train and through the water below when the train is slowed, or... upon death.
Mob strength and mechanics scale with role count; a split Tank-Healer party, for instance, would see different attacks and schema from mobs that a lone healer or a DPS pair. Until one attacks in the mirror world, they will not be noticed automatically, but each will attract attention, making it nearly impossible for the team to simply all die, mob-skip, and continue through. As the lone member on the other side, one can peer back through the mirror to see what's going and sense what's going on in the other plane via the Duty Action, and will primarily act as a saboteur. A conversation with someone in the mirror world, before they were yet wary of you, can change the positioning of a guard in the other, etc. The boss fights themselves are incredibly difficult, and while they do not quite scale like the mobs, the clues and sabotage from the other side can make up for the difference.
There's a lot to manage here, so the dungeon does not take part in typical Expert roulettes (at least as they stand now), but does have its own further weekly reward (e.g. a Fragment of the Interstice, used for upgrading any piece of gear -- such as via 1 per accessory, 2 per armor, and 3 per weapon).III. A strategic assault.In this one, you're piloting your own airship, attempting to find a Garlean supply ship and retrieve from it... (name your MacGuffin). The dungeon is reiterative and allows you to offset eventual difficulties with further exploration. It can mostly be split into three phases: (1) find the key airship while surviving against anti-ship and boarding attacks from other ships, (2) board the key airship and seize the MacGuffin, (3) escape back to the airbase. In a premade group, the ship can be steered manually; otherwise, you just yell orders at the helmsman (who is also a decently strong combatant whose power scales with party and who swaps with him in premades). The first boarding attempt will count as the first "boss fight", but its mechanics vary greatly. The second is on the enemy ship. The third is in the escape. There's a further 5 optional bosses in the dungeon. The premade experience is, in essence, the intended one, though the fights themselves can still be damn fun even when the dungeon is streamlined.IV. RNG-ish-pathed dungeon.So this one's actually an 8-man, along the lines of Praetorium or Castrum Meridanium, but this time with a pre-entry strategy session that will, at player choice, determine how one goes about progressing through the dungeon and in what groups. That said, the circumstances in the base change each run. While these patterns, too, can eventually be optimized by veteran runners, this offers a further degree of variety. There's a fair bit of behind-the-scenes work that goes into determining player weights in these deliberations. For instance, the more clears a player has, especially if as leader, and weighted by the 'quality' of those clears, the more likely they are to be picked as commander, lieutenant, etc., giving them further weight in that decision making. The fewer people joined together, the more these prior deliberations are simplified, while larger premade portions make for more freedom and precision.
The mechanics involved can go anywhere from creating distractions, stealing key cards, turning off sentry lights, stealing mechs, stealing an airship, raiding the armory, blowing holes in walls, sneaking in via the train, killing the ceruleum lines, etc., etc. This, too, will be side-content for weekly rewards, not a mainstay dungeon.Imagine a large Monster Hunter World-esque Jungle Ruins area with four distinct regions and a final boss that swoops down to the center area after most of the other bosses are dealt with. You'll start off in one corner and depending in part on how you fight the boss of that corner, different paths will appear. For instance, if you have the... let's say it's a triceratops boss... crash into a pillar, you can have him open up the way across the chasm, but then his death animations won't lead to him opening something up later, etc., etc. Each boss's defeat grants you a boon or upgrades a preexisting one. These can be used via the duty key, either under different conditions, or where the last one acquired must be used first to then reveal those beneath (where the new don't simply upgrade the old). For instance, the triceratops-ish boss might grant a tackling charge, driving enemies back while being used for mobility, while the... (spitball) one-winged harpy might grant temporary casting while moving alongside quick bursts of movement to your left. There's obvious faction warfare, so to speak, between the minions of the different boss zones, so managing that plays a bit of a part, too.
Basically, pathing semi-choice, gameplay augmentation, macro-level mob management, and an optional fourth core boss to make the final boss easier.