I'm running a homebrew of Monster Hunter as a first time DM, with sort-of first time players. They treat it like a Disneyland ride where they "go here do X" and so I set them up for the first major boss fight with Teostra (cr13) against their group (lv4) with the inte t that they do 1/4 to 1/2 it's health to drive it away. (I know they can't kill it).
Except rather than fight it they offered to make it a cooked meal, since it can speak draconian and I want them to actually try to roleplay I let it unfold. Except now I have no idea how to proceed. I want this to pan out because it's the first time they've all truly put their heads together and had to figure out how to proceed to actually strategize in the way I see so many players just naturally do in podcasts, but in the spirit of MonHun, the Elder dragons are nearly ageless and you cant...just like reason with them.
I also have no way to set a scene other than pure improvisation for this "city saving cookout" they have to plan. Help?
Let it play out - if they come out of their shells and RP, they'll make it interesting. And if they save the day w/o a fight then you've got something in your library of encounters to pull out some other time when in need.
As for how to run to cookout: Let them figure out party logistics, but be ready to be an NPC or two that jump in with suggestions. Think through the things they'll need (food, drinks, guests) ahead of time and come up with some options if they ask the right questions. Maybe someone knows of a local pig farmer who'll trade some pork for an IOU from he party.
Then think about how Teostra may respond. If they make friends then maybe Teostra reveals that he has been talked into hunting the party because ____. That can set you up for your next adventure. Or two adventures, counting the pig farmer.
I think your players have an awesome idea, and it would be a good idea to lean into it. However, you took the time to prepare the encounter, and as the DM you're playing the game too and you all deserve to have fun together.
Now we're talking about cooking a meal fit for a force of nature. You're not going to be satisfied with a simple sandwich or a grilled steak. No, you're a dragon, your palate deserves to be graced with meals that surpass those given to kings of men.
Here's a couple ways I could see that playing out
Teostra wants some exotic meal made with ingredients that are rare / magical / dangerous to procure
A dragon eats its kills, and has a taste for monsters. The wilder and stronger the better
The dragon is presented with a meal but is unaccustomed to the seasonings. Maybe it has an allergy, or it's too spicy, and this enrages it. Then you still get to have your fight with Teostra while the party tries to calm this fit
In another comment you said that the dragon was motivated to destroy the village because it's in the way and it wants to see something new out of curiosity. Even if the party gives it a fantastic meal, these things are ephemeral and I think Teostra will have wanderlust again at some point. So I also wouldn't think that cooking a meal would be a one-and-done situation, and maybe they'll have to continually parley with the dragon. That in itself might be amusing enough for a dragon not to destroy all humans, but hey, it's a dragon so maybe not
Do I let them or do I push the fight I set up? I don't even know what rolls to call for lol
I want it to be fun, that's my job as DM.
What DC do need to be asking for? A lot of them have +5 or more in some of their Skills, and +3 in attributes. I want these Elder Dragons to be Deadly Encounters.
What's the motivation for the Elder Dragon to fight the PCs? Is the Teostra here to kill hunters and can't be swayed? Will it accept the meal and let them live if they never return if the food is good enough? And threaten to kill them if it isn't satisfactory? Does the Teostra see an opportunity and decide to hire them to take out some lesser monsters that have been bothering it but hasn't found the time to deal with yet. Perhaps eventually it asks them to even take out another group of hunters.
You can do multiple skill checks for encounters. Persuasion to see if the Teostra will not immediately fight and consider their food. A cooking utensil check for how impressive the cooking turns out. The Teostra is an Elder Dragon so the DC for checks could be set high, but up to you ultimately.
Personally I'd probably have something else (Nergigante or Kushala maybe) crash the party and make Teostra into a temporary ally, then if the fight goes well make him a permanent one. He'd never join the party for real, but there would always be the option to have him jump in for the occasional big dramatic set piece.