If this thread works out we should add some of the information to the Wiki.

I'm sure this interests almost everyone, because sure who doesn't like watching a big tussle. Well, I want a large battle, and I don't care if the engine doesn't handle them well, it doesn't have a choice. I've been reading and experimenting a lot with the feasability of doing it for a while now.
There are loads of little tricks that can help improve FPS during a battle scene. So what I'd like to find out is what is the definitive list of techniques available to modders to achieve the feeling of a large battle while keeping the game playable.

So far I have explored No Low Level Processing (AI), Subspaces, SetSceneComplex (Function), have a limited number of NPCs/Actors fighting and replace when dead. Anyone who can please contribute you own ideas, techniques, or elaborate on ones already mentioned.

You should ask/look into Soran('s threads) about the same - They should have some reliable info,

Offhand:
@# Make the scene as simple as possible, preferably with an open, non-obstructed playfield.
@$ Make use of actors which use the same base ID as much as possible. Even aside from the duplicated equipment, processing is saved by the instanced faces, combat styles, and AI packages.
@ Full head helmets. Often overlooked, these can save on framerate issues as most full helmets contain less detail than the face/hair beneath.
@$ Make use of dense fog and if possible switch object views (OBSE) to distances near the edge of that fog during the scene.
$# Creatures require less processing demand than NPCs, and due to the size of some being larger, can work well for filling a battlefield.
$# Scripted combat as opposed to AI/Disposition controlled. While it might seem contradictory, having opponents scripted to start combat instead of waiting for their AI to update can ease both performance and smooth over the look of the battle. This should however still be backed up by a clear disposition based hostility between participants.
@$# Limit any magic use to scripted behavior that is all controlled by a single script. Not only does this mean giving actors a less complicated combat style, but also diminishes the amount of memory needed for each instance of that actor as they don't actually need that spell in their list nor the skill and mana to use it. The usage is also subject more directly to how the scene is being processed instead of having to be handled by each individual actor.

Key
@ Graphics optimization
$ Processor optimzation
# General playability and reliability

Contact the MERP team
We are working on it, and I'm sure that the ones responsible is very interesting to learn how

So far I understood that they would create some animated meshes/pictures in the distance so it looked like there were a lot ;D and then just keep sending 20 NPC's at the player or something like that