Escape the Underworld plot help

I’m DMing my first campaign (5 people including me who have never played DnD before) and I accidentally TPKed my party. Instead of ending it, I set them up with an escape from hell plot as the session ended, but I don’t think I know enough about official DnD lore to run this. I did have some ideas going in though.

1) Ghosts from their past, obviously. 2) They are currently level 2, and I plan to have them level up once or twice over a few sessions. 3) A strong monster that they probably won’t be able to beat, but it’s right by the River Lethe so they can push it in and convince it that they are friends maybe (like Iaeptus/Bob from Percy Jackson iykyk). 4) The final fight is a mirror fight because their souls were split but idk why they’d be split yet

Any advice or tips would be appreciated

Greetings SGB905,

If you are looking for good lore on the Nine Hells, there are a few books I'd suggest, but don't know if you have access to them:

• 2024 DMG: Has a decent section on the Nine Hells, including a description of each level, Infernal Hierarchy, and a few paragraphs on Nine Hells Adventures.
• 2014 DMG: Has the descriptions of the levels of the Nine Hells.
• M: Tome of Foes: Has an entire chapter on the Blood War, which goes deep into the Lore of the Nine Hells, the Devils that rule each level, and the full makeup of each level.

Hope that helps :)

If I were you I would think first in which of the evil aligned Outer Planes they ended up (did they awaken in the Nine Hells, Hades, Carceri... maybe Pandemonium?) and read up about the lore of that specific place to fuel your creativity. An interesting feature for them could be the river Styx, which flows through all of these planes and usually has ferries on it which allow you to travel through various planes. All Outer Planes are connected to the Outlands via something called "gate-towns", so you could have them go around and looking/asking for a portal like that. In the Outlands there is Sigil, a city that has portals built in it for every place in the multiverse, and most likely they could also find someone which tells them how to get their souls reconnected to their bodies. Or they could travel to one of the good aligned planes (like Mount Celestia, Elysium, Arborea etc.) to find a good samaritan or celestial creature to help them out, as I'm sure they'd be happy to help them if they weren't bad people in their past lives. 

For the final fight, careful making their mirrors exact copies of them, as they might just TPK again from that haha

Hope this helps! :)

Not much in the field of mechanics but you could look at HADES by supergiant games, its a rogue like with that same premise, you could draw inspiration from there  https://100001****/

Whichever plane you choose, I would ask how the characters' souls ended up there. Something for which D&D has some interesting (though rather convoluted) lore.

The Shadowfell: As I understand it, any soul risks being grabbed by the plane of undeath before it has a chance to reach the Outer Planes. Of note is that there is a place in the Shadowfell called Letherna, which contains the Raven Queen's Fortress of Memories. If you are looking for something that feels like the classic mythological Hades, the Shadowfell might be better at it than the plane D&D calls Hades.

Divine Dominions: If the characters share a strong faith in a given deity, that would explain their appearance in said god's private afterlife. This divine dominion could either be floating in the Astral Sea or occupy a region within a layer of one of the Outer Planes. In any case, the deity decides how the place works.

Outer Planes: Without interference from the Shadowfell or from a god, a soul goes to the outer plane that shares its alignment. The Outer Planes number seventeen, or sixteen if you count the Outlands separately, covering various shades of law, chaos, good and evil. Where it can get confusing, when compared to classic mythology, is that the names Elysium, Acheron and Hades are used for three distinct outer planes instead of Elysium and Acheron being part of Hades. Furthermore, most planes have multiple layers such as the Seven Heavens of Mount Celestia or the Nine Hells of Baator.

By 5e Planescape rules, a soul that arrives on an outer plane becomes either a celestial petitioner or a fiendish petitioner and, at least at first, retains the general appearance of its mortal self. However...

The River Styx: Souls arriving on an outer plane on account of evil alignment alone will first appear inside the River Styx, which in D&D shares the River Lethe's memory-stealing properties. The memories turn into sediment at the bottom of the river while the amnesic soul emerges as a weak fiend, such as a lawful evil lemure, a neutral evil larva or a chaotic evil manes. A soul's faith in a god, even an evil deity whose dominion is technically part of an evil outer plane, might allow that soul to at least avoid the Styx and manifest as a regular fiendish petitioner. A similar effect is obtained if a character entered a pact with a fiend. Devils in particular like to collect souls that have not lost all their skills to the Styx.