Advice for large groups

[Twixman]

Hello all, still in the planning stages but I need some advice on how to run a large group game.
I just want some general advice to keep it as simple and painless as possible. The number is not a definite but eighteen people will be invited. I will have a Co-GM to help with things. Its for D&D 3.5, its a one time session muck around. I was thinking of making them fifth level, though if the majority says a little lower is better then that will change to about third.
Thankyou in advance for advice, tips and potential pitfalls. I fully understand that it may will in all likelihood be very, very difficult though I am perfectly willing to put my all into this.

[eviljav]

A few quick suggestions:
1). Ask people to avoid using summoner/minion master-type classes - if they're dying to play one then, ok, but ask them if there's something else they'd consider.
One summoner can be a pain, as far as book keeping. 10 will be a nightmare. 18 Druids/Necromancers/Conjurers ... I shudder to think about it.

2). Be careful with your monsters - something that's appropriate CR for 18 characters will likely kill a few characters per round. So, aim for enemies with lots of minions, even though this is a book keeping nightmare.

3). All the tricks to save time per round - tell everyone to have their spells (including full descriptions) available. Roll to hit and damage at the same time, etc...
If each person takes 30 seconds, you're still talking about ~10 minutes between each action per player.

4). miniatures/battle mat- with that many people, understanding positioning is really hard. You're talking about tracking more people than one side of a chess game.

5). Probably aim for more "hack and slash" - detailed plots and interaction with NPCs will get bogged down with that many people.

6). Delegate "snack duty" to a few people.

[Enguebert]

CR is related to a group of 4 people

If you have more people, don't increase CR but increase nbr of monsters

For minions, easy : for 16 people, mutliply them by 4
For leaders or powerful solo monsters, it is more diffuclt (not easy to justify 4 leaders :-)
In this case, i usually increase level of leader by +1 or +2 and add lieuteants who are level +0 or level -1

Also, for such a large group, you will need very large battle map.

Probably no dungeon or undergroup complex, but wilderness area or whole village battle will help.

If you have a co-gm, to speed up battle, you and your co-gm manage one side of the battle

[Twixman]

Thankyou
Didnt even think of battle maps.

[Fouredged Sword]

Yeah, fights are going to have to consist of massive groups of monsters that fall into four groups.

A - Bosses - Not every fight needs a boss, and some have 2 or 4. This is the big monster the party is fighting, and it should be powerful enough to hurt a player (for more than half hp in damage), but not kill them.

B- Guards - These are tough, but not necessarily strong fighters who delay the team from bringing all their resources to bare on the boss all at once. Take something normally CR-1 or so and double the HP.

C - Shielders - These are minions who are weak, but restore condition to the boss and guards. Think clerics and such. Your boss, no matter how tough, won't be able to fight after 9-10 save or loose spells. These guys act to pick the boss back up to fight some more.

D - Minions - Quick to die, weak, and plentiful. Seriously, just give them all 1hp and evasion.

[Endarire]

If this is a one-time, large party event, death is not as much of a concern. Characters can afford to be lower powered compared to standard considering you have so many of them.

Talk with them to determine who wants to do what, in terms of roles and content. Do they want a diplomatic game? Dungeon crawl? Hack-a-thon?