help requested - ideas for a large group one shot game

[atomicwater]

Hello im throwing a d&d 3.5 party for my b-day and i do one every year because from what i find everyone enjoys it.
And this year im having trouble of making a one shot idea that will get my players interested at least. Im hoping somebody can give me some one shot ideas or tips any help will be greatly appreciated.
keep in mind im going to have 8+ people and the last time it was 11.
im thinking to start them at lv 5 -10 premades -with specific goals and allies, personality etc ..
things im looking to incorporate in the game is


possibly a classic battle between good and evil

at least a chance of pvp for rp reasons and fun

challenging riddles ,traps ,things to make you think

a fun challenge with twists and turns that has many opportunities for good rp and possibly backstabbing

at least one player who plays a evildoer and one good person at least ,or teams of evil and good but no one knows who to trust etc..

if you can't get all of them its fine , all i need are some ideas and tips and again any help is greatly appreciated

[Ssalarn]

You could always steal a little inspiration from the Sundering event taking place in the Forgotten Realms lore right now leading up to 5e and do something like:

The characters are each the Chosen of a specific deity (give them a specific SLA representative of their deity's particular nature) and a powerful lich has trapped them all in an Undermountain-style labyrinth filled with traps and monsters designed to bring out their divine abilities and then harvest them. The players have to find their way out of the labyrinth, but along the way they also have chances to come into conflict with other players whose deity's goals or interests conflict with their own. Depending on how PVP you want it to get you could even have the players discover that they can harvest the divine sparks from the other players to enhance their own abilities, making them stronger and increasing their chances of being one of the ones to survive and escape the labyrinth. Players who make it to the end will find themselves in a battle royale against a lich who has collected the powers of every character slain by the labyrinth's monsters or traps and added them to his own formidable array.

[Captnq]

Another Day On The Bridge
In the capital city Kingshold of the nation of Inverness, the sky is azure blue, the sun is always shining, the weather is mild, the streets are clean and the people are among the most intelligent and powerful in all the world.

You are as far from Kingshold as is humanly possible.

And I mean the word "humanly" because any further and the humanoids will kill, cook, and eat your ass.

For whatever reason, you have found yourself up at Skybridge, the outpost where careers (and people) come to die. Solders who pissed off superiors, criminals given banishment as an option, and debtors who required to take whatever job offer they are given all wind up at skybridge.

Why is it called Skybridge? Because it's at the top of a damn mountain, that's why. Crafted by dwarves eons ago, the bridge magically remains free of snow and ice all year round. Which means that the humanoids to the north of the bridge want to capture it and use it as a staging area to attack Inverness. Your job? Hold the bridge. If you last a year, your replacements will come and you will get to leave. Some of you get paid. Some of you just get to keep the clothes on your back. Eitherway, you won't have to stay here.

Encounters:

Captain Magog: the overweight coward who makes boatloads of money smuggling goods to the north to sell to the humanoids. They pay 3 or 4 times the price of the same goods as to the south.

Escaping Co-workers: Some of your fellow guards choose to flee. You are ordered to hunt them down and kill them, then return, or you will be hunted down and killed. A Mark of justice is put on the leader of your group to encourage him to make sure this happens.

Monster attack: Occationally cold monsters come to the warm bridge to roost. Someone needs to chase them away.

Secret Cave: Someone falls off the bridge. You have to find the body. Whoops! Secret cave!

Humanoid Attack: Yup. They actually attack. Why? Captain Magog screwed them. He kept the goods he was selling AND took their gold. Now they want revenge and their agreed upon goods. Magog offers you a cut of the profits if you can but hold off this assault. Can you trust him? Can you defeat the humanoids? Can they figure out how to use a ballista without killing each other?

TUNE IN NEXT WEEK FOR THE EXCITING CONCLUSION TO:

Another Day On The Bridge!