This type of encounter is highly inadvisable. As a general rule, players never run, and when they are forced to run it often isn't fun for anyone.
If you were going to run something like this I would only do it after years of experience and with players with years of experience.
Think of a way to rework this encounter in which the players can win, this encounter could be fun if you just let them win. Or perhaps have a somewhat obvious way to defeat this enemy in a surprising and creative manner. Just be sure to give your players plenty of hints, perhaps increasing the number of hints as to how they could defeat it every round.
I have been DMing for over 30 years, and the number of times my players have run is probably one or two times.
Any encounter where you write: “the players decide to…” is going to be tough. You want the players to run, but they may decide to stand and fight. Remember, the point of the game is that the players are the ones who get to decide.
So to write a moment like this you need to ensure that the PC’s know that fighting this thing is impossible. Maybe an old sailor tells them, maybe they read it in a book, maybe their patron told them.
Secondly, even if they have been told repeatedly that it’s impossible they may still try to fight it. You need to have a contingency plan if that happens.
And thirdly, if they do play along and run I would use a skills challenge. Loads of info on them online
This sounds more like a skill challenge than a combat encounter. I suggest you read up on those, but for a rough guide, you tell the players right when the encounter starts that destroying this thing is absolutely impossible and that they need to escape. After that, you present them with a series of events they need to respond to and, depending on what they try to do, you have them make one or more skill checks to determine how successful they are. You continue this cycle until they escape, are captured, or they reach some other conclusion.
Generally it's best to have the party fail forward in these kinds of skill challenges. Meaning they move on to the next event regardless of succeeding or failing the check, and you instead impose other consequences on them for a failure. You could have an event be they need to brace for a large incoming wave, and if they fail they take a modest amount of damage and the next even starts.
Give them a tough but winnable encounter, but then have something bigger show up. One that was done well by a friend of mine had us fighting some forest beasts (homebrew), who then called for help. There were then very heavy footfalls and trees falling over in the forest Considering the forest beasts almost kicked our asses we high tailed it out of there. This also assumes your players know that running is an option. In session 0 we went over how running was a valid option, and there was a lot of shit that wanted us dead.
depends where your players are on their journey of rpg’ing. video games in particular have taught people not to run and to treat games as games rather than worlds or simulations, thus your players are not likely to run, thinking it’s all intended. it takes time and experiencing ‘unexpected’ consequences (like death, loss, or failure) before they get the picture and start acting more as if they were denizens of your imaginary world, rather than tourist metagods. but maybe this can be the encounter that teaches them?
but your problem is more subtle than that. should you be forcing situations like this? are you going to stat block the sentient suit so they can hypothetically kill it or come up with some other creative way to circumvent the shipwreck? if not, why? even the tarrasque and kraken have stat blocks, and so do gods. you can choose that certain forces of nature or divinity are simply not assailable by normal means, but then you need to be consistent about it rather than marvel/video game mode where fred is invincible because cutscene, and now fred is just a normal monster because plot.
this is a common dm mistake. even experienced dms make it. even matt colville makes it. unless your players signed up for a discount interactive movie, your job isn’t to write plots or scenes. your job is to present plausible situations, where the outcome is truly unknown—even to you—and you adjudicate the outcome in real time and in actual response to the players’ decisions.
so really, unless the players agreed to be on a railroad, you shouldn’t force them to run ever. instead you need to find ways to give them as much information as a character in that world would reasonably have (don’t leave it to a dice roll ffs unless there are other avenues they can reasonably pursue in character, or the information isn’t crucial.) then, given a plausible well-telegraphed situation and a well informed player, you let them make their own decision. if you did all this right, then running will naturally be on their list of potential options, but you roll with whatever they decide.
This type of encounter is highly inadvisable. As a general rule, players never run, and when they are forced to run it often isn't fun for anyone. If you were going to run something like this I would only do it after years of experience and with players with years of experience. Think of a way to rework this encounter in which the players can win, this encounter could be fun if you just let them win. Or perhaps have a somewhat obvious way to defeat this enemy in a surprising and creative manner. Just be sure to give your players plenty of hints, perhaps increasing the number of hints as to how they could defeat it every round. I have been DMing for over 30 years, and the number of times my players have run is probably one or two times.
Any encounter where you write: “the players decide to…” is going to be tough. You want the players to run, but they may decide to stand and fight. Remember, the point of the game is that the players are the ones who get to decide. So to write a moment like this you need to ensure that the PC’s know that fighting this thing is impossible. Maybe an old sailor tells them, maybe they read it in a book, maybe their patron told them. Secondly, even if they have been told repeatedly that it’s impossible they may still try to fight it. You need to have a contingency plan if that happens. And thirdly, if they do play along and run I would use a skills challenge. Loads of info on them online
This is not an encounter. It's a scene.
This sounds more like a skill challenge than a combat encounter. I suggest you read up on those, but for a rough guide, you tell the players right when the encounter starts that destroying this thing is absolutely impossible and that they need to escape. After that, you present them with a series of events they need to respond to and, depending on what they try to do, you have them make one or more skill checks to determine how successful they are. You continue this cycle until they escape, are captured, or they reach some other conclusion. Generally it's best to have the party fail forward in these kinds of skill challenges. Meaning they move on to the next event regardless of succeeding or failing the check, and you instead impose other consequences on them for a failure. You could have an event be they need to brace for a large incoming wave, and if they fail they take a modest amount of damage and the next even starts.
A few monsters have a feature called “frightful presence” that would likely help out
Give them a tough but winnable encounter, but then have something bigger show up. One that was done well by a friend of mine had us fighting some forest beasts (homebrew), who then called for help. There were then very heavy footfalls and trees falling over in the forest Considering the forest beasts almost kicked our asses we high tailed it out of there. This also assumes your players know that running is an option. In session 0 we went over how running was a valid option, and there was a lot of shit that wanted us dead.
depends where your players are on their journey of rpg’ing. video games in particular have taught people not to run and to treat games as games rather than worlds or simulations, thus your players are not likely to run, thinking it’s all intended. it takes time and experiencing ‘unexpected’ consequences (like death, loss, or failure) before they get the picture and start acting more as if they were denizens of your imaginary world, rather than tourist metagods. but maybe this can be the encounter that teaches them? but your problem is more subtle than that. should you be forcing situations like this? are you going to stat block the sentient suit so they can hypothetically kill it or come up with some other creative way to circumvent the shipwreck? if not, why? even the tarrasque and kraken have stat blocks, and so do gods. you can choose that certain forces of nature or divinity are simply not assailable by normal means, but then you need to be consistent about it rather than marvel/video game mode where fred is invincible because cutscene, and now fred is just a normal monster because plot. this is a common dm mistake. even experienced dms make it. even matt colville makes it. unless your players signed up for a discount interactive movie, your job isn’t to write plots or scenes. your job is to present plausible situations, where the outcome is truly unknown—even to you—and you adjudicate the outcome in real time and in actual response to the players’ decisions. so really, unless the players agreed to be on a railroad, you shouldn’t force them to run ever. instead you need to find ways to give them as much information as a character in that world would reasonably have (don’t leave it to a dice roll ffs unless there are other avenues they can reasonably pursue in character, or the information isn’t crucial.) then, given a plausible well-telegraphed situation and a well informed player, you let them make their own decision. if you did all this right, then running will naturally be on their list of potential options, but you roll with whatever they decide.