Hey there, I just need a few opinions and ideas here. Basically, I want to try to do a longer one-shot with a time loop mechanic. I read through a few threads about this and I think I came up with a decent way in which it could work, but I am afraid to overlook something, so I am looking for some advice.

-The Setting is going to be a flying Island since I want to restrict the players and myself a bit on possibilities.
-I want to implement checkpoints, so players do not have to convince the same NPCs all over again.
-The time loop is only one day long and ends with a catastrophe, right before the PCs  die since:
-I want death to have an impact on them, so I want to implement them losing their memories in the case that they die so they don’t throw themselves endlessly into battle (The problem is their characters won’t know that they died, but maybe I can implement someway they notice a loop has passed so they know their plan didn’t work).
-The BBEG is also excluded from the time loop and tries to end it to make the catastrophe permanent, my players are stubborn and I know without any time limit they will try to convince the same NPCs over and over again, so each time loop the catastrophe might start differently or a bit earlier, so they don’t get too comfy in the loop.
-Another idea I was playing with which I might implement depending on how it’s going: basically the time loop needs energy sources to work, and if one of them gets destroyed by BBEG, the loop will not start in the morning but maybe at noon, leaving them with less choices to make and less time to make them.

A Problem I have is: if my players get stuck somewhere and don’t know where to go, how do I help them? In the past I just sent them an NPC to set them back on track, but in a time loop that’s not really possible. I can set aside one NPC and send them with Info, claiming he is every time loop just looking for them and only found them this time because of what they did in that loop. But maybe there is a better way?
Also, I am not the most experienced DM, please be honest if you think this is an idea better put on the shelf until I am more experienced.

Sorry for any errors, I play a different language but I hope I used all the English terms correctly and thank you in advance for any thoughts or advice!

Hey! Explore your idea. But I think I can help. You seem to be getting locked into the idea of endless boring repetition. This can happen easily, but at the same time, do you really expect that your players will actively refuse to metagame the entire time? They will be acting on knowledge they aren't supposed to have, it happens on a subconscious level, they would have to be advanced players to actively keep from doing it.

So here is my suggestion. When the time loops, introduce "butterfly effects" to little alterations the character make, make little changes a big deal. Make them logical, and predictable, but maybe a bit inflated. This will avoid repetition and allow for additional plot elements to be produced in the replays. The actual movie "The Butterfly Effect" displays what I mean. Terrible movie, but the plot mechanic is I think what you are looking for. Cheers.

if you get a chance there's a DM guild adventure called "the last day in Sharn" which operates on a similar premise might be worth a read to give you ideas.

basically, the party get time bracelets that are tied to a point in time before the catastrophe (the person who gives them is from the future and tying to prevent the disaster)

when players die they go back to the same point again and again. when players reach a check point to represent them having to reach the some point again, use skill checks to condense there efforts, on a fail, they get exhaustion

if one player dies they take a skill test then turn up in the next scene, they were always there but because of the overlapping the timelines the party remember both the player being there and not being there (bit of a hand wave but prevents the party getting split in different locations and times