A little town.. with a secret

[edised]

I had a idea, vary Unpolished, of a small town domain that travels, a poket domain

The idea is this, the town is rather rural and out of the way a step up from a one horse town but not by much. It’s not a bad place, rich history and a steady industry, just not “exciting”.
Now being out of the way there was one town doctor/wizard but they were getting old. Looking to the future, they found a young rising star, the smartest teenager, the town pooled there money and sent him to university in the city so he could be the new doctor/wizard. This was a mistake, the university was a challenge, and others did better than him, city life was both overwhelming and captivating, he made bad choices and partied to much. But he managed to pass just not vary highly, by this time he resented his home and there expectations, he even imagined just never going home.
He did go back to his home town, and everyone celebrated, he was treated like a hero, everyone was so proud, he seethed he only came back because he had little choice. As time went by his hatred grew, other university friends were making a name for themselves and he was stuck here.
He started to sabotage other’s lives, spreading rumors, he even destroyed a marriage telling the wife her husband had a std from cheating (it was a rash from new soap). If he was miserable everyone will be miserable. It came to a head when he started a small fire, only it did not stay small, as he looked on as anarchy consumed the town the smoke swept over him only to realize it was mist.
The town is in a cycle, it will change its aspect but always be a small town with a vital industry out in the country, the town folk will change their history and roll (a mean old farmer may become a jovial shop keeper), but always there are secrets going on and eventually a town wide desaster will strike and the dark lord is the last to die then everything will reset and change (like a secret werewolf pack kill everyone and another time there are secret werewolves but the real danger is the postmaster decides to go postal with explosives)
The dark lord is the only one to remember the change but also the only one not known the new history and it’s driving him crazy.

[TheArcaneWeirdo]

interesting.

[TheArcaneWeirdo]

I like how the darklord is on the one hand relatable, and on the other hand still responsible for their evil. Their anger is understandable, but they still very much chose to be jerks. It's a balance that's hard to do correctly.

The biggest chanllenge here is how to expand the lore.
If I understood correctly, you're aiming for a town with history, social dramas and mysteries rich enough to give background to an adventure - that can be replaced in a moment. The DM would need not one description of the town, but a system allowing to generate multiple versions of it.
I'd recommend to invent a few npcs and locations that always reincarnate and always have significance, and give each a random table with suggestions as to what could be their role in this incarnation. (If you want to add extra depth to the design, I'd suggest to explore the concept of tropes, archetypes etc - elements in storytelling that repeat themselves in different guises. I won't tell you what to do, but think what sort of things changes and what stays the same.)

And one more question:
Is there a base case?
As in, a condition that stops the loop?
Cause a lot of darklords have a reincarnation mechanism, but I think it's a lot more interesting when there's a way to cut it off. Revealing Saidra as a fake noble, breaking the cycle of domestic abuse in the Hiregaard family, exterminating Kartakass' dire wolf population...
It turns the curse into a puzzle, a mystery on it's on right that needs to be solved.

VIEW CONTENT:

As with any DND puzzle players are ought to have their own solutions and the DM needs to be willing to acknowledge their creativity, but I have a suggestion:
An interesting point about this story is that the darklord-to-be did what they did due to feeling stuck, but they never really were stuck. They could switch to a degree that actually interests them. They could quit the university. They could not return to town. The town would find another doctor/wizard, they'd be fine.
The darklord chose to remain on the path paved for them, the path they never wanted and were never forced to walk in, out of convinience - to not make a scene, to not displease their elders, to not pay the price of change - then got pissed off.
What if this never changed?
What if contrary to most, this darklord can walk out? Always could? Nothing forces them to stay in the domain. In every single incarnation, they have a chance to leave the town. It's always challenging and inconvinient, but never out of reach. It's always their choice - they just need to stop raging over the life they don't want and start working towards the life they want.

[edised]

Oh I like that, also the dark lord has a a sense of guilt, thay where given a opportunity and had high expectations but they failed (if only themselves, they barely passed there class’s), partly because it was harder than they expected, partly because in the city there are many distractions not seen in a small town. The guilt turns to resentment, and then hatred, they let it fester and he hurt the people who loved him.