I originally planned to run "The Isle of the Abbey" from Ghosts of Saltmarsh, but I got inspired and started modifying it heavily. Now I have come up with a radical twist that I need some help working out.

Here are the simplified details:

- The party fails to prevent the summoning of a beholder in the catacombs under the abbey. If not stopped, the beholder will activate its tyrant ship and annihilate the nearby city.

- The day before, they found a mind flayer skeleton holding a mysterious amulet with two buttons - purple and orange. A ghost of a mind flayer appeared to one of the players in a dream and told him to press the purple button to "CAPTURE".

- The party engages in battle with the beholder. Being level 5 characters, they're all going to die horribly. (This will be a fun time for the DM to let loose.)

- At the moment of their deaths, time rewinds back about 10 minutes. The party has full memory of being killed by the beholder.

- They fight the beholder and are killed again. They realize that the amulet has trapped them all in a time loop where they are forced to die over and over, but the silver lining is that they have trapped the beholder as well. If the players refuse to fight, the beholder destroys the city and then hunts them down and kills them. 

- Eventually the beholder, being an aberration, realizes that time is repeating itself. When it attempts to capture the party, they hit the orange button which sets off a mini nuclear explosion, killing everyone. 

- Finally the beholder and the party have to make a deal to let the beholder go in exchange for it not destroying the city. 

My questions:

- I still haven't figured out how the party can ensure that the beholder won't return and kill them once it's free. Are beholders creatures of their word? Is there some plausible way they can keep it away?

- If you were a player, what would you think of this adventure?

Thanks for reading!

Given how far you're going to really make this your own, I'm going to say that the correct answer is that beholders behave however you wish. Just like it's not the best idea to run monsters all with the same HP, more often that not giving the enemies your party will encounter their own motivations and behaviours will add depth to the world. Going by the books though they are lawful evil so I'd say they're likely to keep their word.

As to the overall design, as a DM and as a player I think I'd pretty much hate it. It's too linear and too on rails. It sounds cool yeah, but if you've got any level of unpredictability in your party the real question is why wouldn't they just walk away from the city? What happens if they never actually find the amulet? What if they press the orange button first? What if they don't press anything until they've spent the time to identify it and how it works? It's the common trap a lot of us GMs fall into at times. We create a fairly decent route to navigate through a challenge but forget that our players are unpredictable and are in a world in which (nearly) anything is possible. It's rare a party will refuse a quest hook outright, but I have had it happen. This outline feels like exactly that.

My advice in this situation is to ask what's the important bit here? Are you looking for an opportunity to wipe the party (but not really)? Are you wanting them to do some deal with a monster beyond their ability to defeat? Are you wanting them to experience a time loop?

Once you know what the important bit to you is, then the rest can actively fall away. If you want the time loop, then the beholder and killing the party is sort of unnecessary. If you want to just kill the party, well it's cheap but have it happen in a parallel or such where they never found the amulet and start fresh next session. If you're wanting them to do the deal with a beholder there are plenty of other ways. 

Don't misunderstand, you've got a great story. It's just I feel like you've left out the most important thing about planning sessions...the party. During planning we lay out the world not the story. It is when playing with our group that the story happens.

My 2cp worth...

Player knowledge might get in the way as Out of Character the players may well know its a Beholder and that they cannot beat it and this then influences their In Character decision and they may well decide to avoid the entire area and then feel off about being made to relive the same few minutes over and over until they try to tackle the big beastie. So, here's a few options:

Have the Beholder do a monologue where the players have the chance to negotiate and see if the Beholder can be convinced to leave the area without destroying the city, this effectively then means they "kick the can down the road" and either come back to face of against the Beholder in a few more levels time or make it some one elses problem.

If comabt is unavoidable, the Beholder has just been summoned and it doesn't have a lair so don't use any Lair Actions and have it "weakened" so it loses any Legenedary actions, can only use one eye ray per turn and maybe reduce the DC of its eye rays down to 12-14 depending on how good your players saving throws are.

For the Timey-wimey stuff, instead of resetting time by 10 mins, give each character one legendary resistance. When thye use it you can then describe time rewinding and using that to dodge whatever eye ray or effect they were targeted with.

That way you can make it a challenge but you have given the players the chance to defeat it in combat and through diplomancy. That said, make sure you leave an escape route as the players might just give up and decide to make new characters rather than fight an unwinable fight for the ump-teenth time.

Quote from Aquilain >>

As to the overall design, as a DM and as a player I think I'd pretty much hate it. It's too linear and too on rails. It sounds cool yeah, but if you've got any level of unpredictability in your party the real question is why wouldn't they just walk away from the city? What happens if they never actually find the amulet? What if they press the orange button first? What if they don't press anything until they've spent the time to identify it and how it works? It's the common trap a lot of us GMs fall into at times. We create a fairly decent route to navigate through a challenge but forget that our players are unpredictable and are in a world in which (nearly) anything is possible. It's rare a party will refuse a quest hook outright, but I have had it happen. This outline feels like exactly that.

To start off, thank you for replying to my thread. 

For the sake of brevity, I left most of the details out of my original posting. This adventure is actually a detour from a larger campaign that has been going on for a long time. The final part of the adventure is linear, but most of the adventure is done sandbox style, with five key locations (originally two), two factions, and three mini-dungeons on the island (originally one).

Here are some bullet points to answer some of your other questions:

• I think they (probably) won't let the city get destroyed for three reasons: 1) they're heroes, 2) it's a city which has been an important part of the campaign, and 3) if they city is destroyed, they'll won't receive the main reward of the quest. That said, if it is destroyed, it won't seriously mess up the main campaign.
• The amulet will be placed on the path to one of their main events. I'll make sure they don't miss it by having the floor break underneath one of them.
• Using the amulet is a little more complicated. When they first find the amulet, the buttons do nothing. Later on, the purple button will begin to pulse, which means it is ready to be used. By pressing the purple button, you are basically "saving your game" to that moment in time. Once they are in battle, the orange button begins to pulse as well.
• The reason for the too-convenient timing is because the mind flayers partially control the amulet.

In terms of my goal for this time loop thing, I want to give the players the experience of meeting a very deadly monster by surprise, losing the battle, but then finding ways to prevail as heroes anyway. Part of the reason why I want to see them lose is that because up until now, our battles have been too easy. The DM that normally runs the campaign won't even send magic users against the party. I want to put the fear of death into them. I also want to let them face defeat so that they can value their level-ups more.

Finally, I want to trick them into thinking that I really did use a one-off story to murder their campaign characters :)

It seems that in terms of changing things, I need to flesh out an alternative route in which they actually do prevent the summoning of the beholder.

Quote from Rob76 >>

My 2cp worth...

Player knowledge might get in the way as Out of Character the players may well know its a Beholder and that they cannot beat it and this then influences their In Character decision and they may well decide to avoid the entire area and then feel off about being made to relive the same few minutes over and over until they try to tackle the big beastie. So, here's a few options:

Have the Beholder do a monologue where the players have the chance to negotiate and see if the Beholder can be convinced to leave the area without destroying the city, this effectively then means they "kick the can down the road" and either come back to face of against the Beholder in a few more levels time or make it some one elses problem.

 

I didn't mention this in the original post but the beholder reveal won't happen until they meet the creature. I'm trying to make it a big surprise. That said, there will be some hints and foreshadowing so it's possible that they'll suspect a beholder.

In terms of fighting the beholder over and over, I plan for most of the rematches to be done narratively. I'm not going to have them do the entire battle more than twice at most. I'm taking inspiration from the final battle in the first Doctor Strange film. 

I don't want them to be able to win this fight with their own fighting abilities, but I'll definitely take your advice on the diplomacy route. 

Thanks for the reply!

Quote from michaelmhiller >>

Quote from Aquilain >>

As to the overall design, as a DM and as a player I think I'd pretty much hate it. It's too linear and too on rails. It sounds cool yeah, but if you've got any level of unpredictability in your party the real question is why wouldn't they just walk away from the city? What happens if they never actually find the amulet? What if they press the orange button first? What if they don't press anything until they've spent the time to identify it and how it works? It's the common trap a lot of us GMs fall into at times. We create a fairly decent route to navigate through a challenge but forget that our players are unpredictable and are in a world in which (nearly) anything is possible. It's rare a party will refuse a quest hook outright, but I have had it happen. This outline feels like exactly that.

To start off, thank you for replying to my thread. 

For the sake of brevity, I left most of the details out of my original posting. This adventure is actually a detour from a larger campaign that has been going on for a long time. The final part of the adventure is linear, but most of the adventure is done sandbox style, with five key locations (originally two), two factions, and three mini-dungeons on the island (originally one).

Here are some bullet points to answer some of your other questions:

• I think they (probably) won't let the city get destroyed for three reasons: 1) they're heroes, 2) it's a city which has been an important part of the campaign, and 3) if they city is destroyed, they'll won't receive the main reward of the quest. That said, if it is destroyed, it won't seriously mess up the main campaign.
• The amulet will be placed on the path to one of their main events. I'll make sure they don't miss it by having the floor break underneath one of them.
• Using the amulet is a little more complicated. When they first find the amulet, the buttons do nothing. Later on, the purple button will begin to pulse, which means it is ready to be used. By pressing the purple button, you are basically "saving your game" to that moment in time. Once they are in battle, the orange button begins to pulse as well.
• The reason for the too-convenient timing is because the mind flayers partially control the amulet.

In terms of my goal for this time loop thing, I want to give the players the experience of meeting a very deadly monster by surprise, losing the battle, but then finding ways to prevail as heroes anyway. Part of the reason why I want to see them lose is that because up until now, our battles have been too easy. The DM that normally runs the campaign won't even send magic users against the party. I want to put the fear of death into them. I also want to let them face defeat so that they can value their level-ups more.

Finally, I want to trick them into thinking that I really did use a one-off story to murder their campaign characters :)

It seems that in terms of changing things, I need to flesh out an alternative route in which they actually do prevent the summoning of the beholder.

 That certainly makes a lot more sense. Obviously when replying context is often easy to miss.

So, if the intent is to put them up against something and allow them to 'fail' in a safe way I think it's a really cool way of going about that. I do think having some alternates might be helpful. I'd still ask the question what happens when the players become suspicious of the amulet, try to sell it, or just drop it as useless? 

Your players, your table might be amazing, but in my experience the only thing predictable is the unpredictability of players. 

Quote from Aquilain >

 That certainly makes a lot more sense. Obviously when replying context is often easy to miss.

So, if the intent is to put them up against something and allow them to 'fail' in a safe way I think it's a really cool way of going about that. I do think having some alternates might be helpful. I'd still ask the question what happens when the players become suspicious of the amulet, try to sell it, or just drop it as useless? 

Your players, your table might be amazing, but in my experience the only thing predictable is the unpredictability of players. 

 If they completely lose the amulet or discard it, I'll probably have to change one of the battles so that they are able to prevent the summoning of the beholder.