getting a party to flee a plot important fight

[Danielqueue1]

IF YOU ARE IN MY CAMPAIGN DO NOT READ FURTHER! YOU KNOW WHO YOU ARE!

looking for a bit of advice here

So I am DMing a campaign where the party is seeking to acquire and protect a certain set of McGuffins (plot devices) they are in a fortress where one is held and the BBEG (villain) has his army attack said fortress. fortress is lost and the Person in Charge tells the Party to take the McGuffin and get out so the BBEG doesn't get it. as the party is leaving. BBEG shows up and tries to stop them.

I want the party to see the threat and choose to make their escape, but seeing as they have had good luck in combatup to this point are Player Characters I suspect they will try to take the BBEG down. now here is where the problem lies.

1 I want the encounter to be between the party and the BBEG and maybe 1 or 2 leutenants
2 The party will have to face him later and I don't want to buff him now or Nerf him later
3 the party has a non-negligible amount of spell casters so 3 uses of legendary resistance can be used up pretty quickly. and banishing the BBEG in round 2 seems absurdly anti-climactic.
4 I want the party to have the feeling that with a little more preparation, planning (and levels) that they will actually have a chance against him later
5 The BBEG is actually doing the same thing the party is doing. Gathering the McGuffins to prevent the real enemy from getting to them. Something that one member of the party is already figuring out, but the rest are totally clueless of.
6 I want to avoid all that "Contractual Boss Immunity"or "Damage sponge Boss" nonsense
7 The BBEG will not let the party escape. is not prone to monologue. doesn't "want a challenge" or many of the common Dumb-Villain tropes. (he does fall in to some of the more subtle ones though)

also I expect the party to face him at level 12 and they are currently level 7-9 so they don't have too long to go.

so I am looking for Ideas, suggestions, things you have done or seen someone do in the past that have gotten a party to flee where they technically could be victorious if they played their cards right and the dice were on their side.

side note. I know there is no Correct answer I am just looking for Ideas that I can build off of, Re-work, draw inspiration from, or some other way fit into the campaign.

[noob]

Maybe that creature is really good at ground control(like prevent all the team from moving) but use stuff against which there is spells that counters easily but that the party have forgotten to prepare.

[1Forge]

IF YOU ARE IN MY CAMPAIGN DO NOT READ FURTHER! YOU KNOW WHO YOU ARE!

looking for a bit of advice here

So I am DMing a campaign where the party is seeking to acquire and protect a certain set of McGuffins (plot devices) they are in a fortress where one is held and the BBEG (villain) has his army attack said fortress. fortress is lost and the Person in Charge tells the Party to take the McGuffin and get out so the BBEG doesn't get it. as the party is leaving. BBEG shows up and tries to stop them.

I want the party to see the threat and choose to make their escape, but seeing as they have had good luck in combatup to this point are Player Characters I suspect they will try to take the BBEG down. now here is where the problem lies.

1 I want the encounter to be between the party and the BBEG and maybe 1 or 2 leutenants
2 The party will have to face him later and I don't want to buff him now or Nerf him later
3 the party has a non-negligible amount of spell casters so 3 uses of legendary resistance can be used up pretty quickly. and banishing the BBEG in round 2 seems absurdly anti-climactic.
4 I want the party to have the feeling that with a little more preparation, planning (and levels) that they will actually have a chance against him later
5 The BBEG is actually doing the same thing the party is doing. Gathering the McGuffins to prevent the real enemy from getting to them. Something that one member of the party is already figuring out, but the rest are totally clueless of.
6 I want to avoid all that "Contractual Boss Immunity"or "Damage sponge Boss" nonsense
7 The BBEG will not let the party escape. is not prone to monologue. doesn't "want a challenge" or many of the common Dumb-Villain tropes. (he does fall in to some of the more subtle ones though)

also I expect the party to face him at level 12 and they are currently level 7-9 so they don't have too long to go.

so I am looking for Ideas, suggestions, things you have done or seen someone do in the past that have gotten a party to flee where they technically could be victorious if they played their cards right and the dice were on their side.

side note. I know there is no Correct answer I am just looking for Ideas that I can build off of, Re-work, draw inspiration from, or some other way fit into the campaign.

I say incentivize fleeing. Have some physical or monetary reward that they probably wont get if they put a risk in fighting. (ex: They are rescuing one person who is so afraid of this place they promise a reward only if they get them out of the fortress safety.) Players will do what is in their self interest, if they save a decrepit old mage they might be convinced to leave the bad guy if he promises some reward to make their characters amazing.

Alternatively pull a star wars new hope, and make them see why they should fear the BBEG. Let your characters see an attack made by some other person and be totally annihilated then the villain and the players get separated somehow (ex: have news that some renowned assassin. mage, or warrior that the players would respect challenged this guy to a duel or something and died.) Maybe they are told a vivid story by an onlooker, or maybe they over hear the BBEG's servants talking about how he disintegrated his opposition. This choice is a good backup as it requires little from you but less optimal because when a DM says an enemy is too difficult some players take that as a challenge.

More options could be provided but the nature and capabilities of this BBEG are not specified, if you could add more info we could better give specific advise as to how the BBEG does certain things. (is he a spell caster, a warrior, or maybe a divine warrior? What feats has he accomplished that everyone would know of? Who fears him and why? And lastly why do the players want him dead?)

Edit: Also I think this thread would be better suited at Forum>Gaming>Roleplaying games>D&D 5e/Next

[Danielqueue1]

for more information about the boss he is a skilled and powerful fighter wielding a "sword of Plot Importance" uses magic items, but can't cast anything himself.

the reason the players want him dead (other than he is the BBEG) is the fact that he hired them, betrayed them, killed one of their close friends in front of them, and left them to die on an island. and to top it all off he never payed them for the mercenary work he hired them for.

[Potato_Priest]

Make sure that when the players encounter him, they're low on resources. I'd take a freshly rested lvl 5 party up against a lvl 20 fighter with a vorpal sword any day, to he honest with you.

[1Forge]

for more information about the boss he is a skilled and powerful fighter wielding a "sword of Plot Importance" uses magic items, but can't cast anything himself.

the reason the players want him dead (other than he is the BBEG) is the fact that he hired them, betrayed them, killed one of their close friends in front of them, and left them to die on an island. and to top it all off he never payed them for the mercenary work he hired them for.

If he's a fighter I'd say make him look like a master tactician to intimidate the party. He should seem one step a head but not infallible. Give him mage advisers to scry for him and lietenants of every specialty to advise him, the mages could help him travel long distances, and defend him while the others could make great mini bosses and future encounters. You could easily say that the BBEG had just walked through a portal to a distant location for his plans a little before the PC's arrive and then have them fight his powerful mage advisers and perhaps a bodyguard of his (assuming they disregard any attempt to stay away, that way they get a fight and a reward if they win but not a party wipe). I must say though some parties might not like having the BBEG being pulled away if that happens just inform them that the BBEG was never meant to be there at this time as he's doing plot important stuff somewhere else.

If they win award them with some items and a quick escape rout out, you can then make it seem as if the BBEG or some of his servants are coming back, the party will probably be worn down from any previous fight and will flee of their own choice. Some suggested methods of escape could be, a magic teleport ring (maybe it only teleports you to places you have been), a flying carpet, a rope out a window, a bag of holding (jump in bag then toss it out window it hits the ground then the party climbs out), a planar gate, or some other useful but not overly powerful method of escaping a bad situation.

[Crisis21]

One possibility is to adjust the BBEG's priorities for the battle. For example: He's not interested in killing the party, just in getting the macguffin. The moment he or one of his lieutenants gets their hands on it, they're out of there. It's a grab and go strike rather than a fight to the death. Have him make this clear to the party when he shows up. Make clear to your players that if they lose possession of the macguffin, they lose this fight. Period.

Now the priority for the party shifts from 'kill the BBEG' to 'keep away'. And assuming your players have any sense (which can be a big assumption for some groups if I understand correctly) they will figure that the best way to keep the macguffin away from the BBEG is to get the hell out of there.

And if they still decide to stand and fight, well I'm sure your BBEG and his lieutenants have plenty of tricks to leave your players short one macguffin and no xp for the fight.