The 'Arena of Death'-type character brawl game thing seems to be reasonably popular, so I thought we might as well use the site to try and codify the rules a bit. From memory, these are pretty much what we've been using. Anything I've missed out/gotten wrong?

Forces

Players can spend 500pts on one or more characters. All characters have to be from the same Fantasy army list and the normal equipment and magic item limits apply (ie magic items can't be duplicated unless they normally could be). Characters may be mounted on anything they normally could be, including monsters and chariots.

Basic Gameplay

1. Table setup: lots of terrain (preferably something like the cave boards). Deployment zones should be spaced around the edges as equally as possible and should be roughly 12" square (ie one cave board).
2. Randomly determine which player starts deploying first (ie number each player and roll a d6/d8/d10/etc). This player picks a deployment zone and places their character(s) anywhere in it. Roll again to see who deploys next (roll d6/d8/d10/etc, reroll players already rolled) and continue until everybody has deployed.
3. After everybody has deployed, roll to see which player starts first (same way as for seeing who deploys first). After the first player has taken their turn, the player on their left takes their turn and so on until everybody has had a turn. Randomly determine who starts first in the next set of turns and keep going until only one player's character(s) is left alive (or undead but still animated, etc). When there are only two players left, stop rolling to see who starts each set of turns and just alternate as normal.

More Specific Stuff

Movement:

• Models move and charge as normal. Single man-sized models on foot move as skirmishers (360 degree charge arc, can always march, etc), larger or mounted models move as monsters (90 degree charge arc, can be march blocked, etc), as per the normal Fantasy rules.
• Flyers can only fly at full speed (ie 20" for most things, 15" for hoverers, etc) if their movement is solely within a cavern. Flying moves not made solely inside a cavern are limited to 10". Cave walls are impassable to flayers (ie you can't fly through walls).

Magic:

• All spells require line of sight to their targets, even if they normally do not.
• In each player's magic phase, the player recieves their normal power dice pool and each opponent recieves their normal dispel pool. When a spell is cast, one player can attempt to stop it. If two players want to dispel the same spell, the player who is going to use more dispel dice gets to make the attempt. Auto-dispel items always 'beat' any number of dispel dice.
• Remains in Play spells can only be dispelled during the caster's turn or the turn(s) of the target(s) affected by the spell.
• Spells can be cast into combat as long as no friendly models are involved. Spells that affect an entire unit will affect all models fighting, hits from spells that do Xd6 SX hits are distributed as shooting hits.
• No additional models can be summoned. This applies to spells like Invocation of Nehek and Indigo Fire, bloodline powers like Summon Bats and Summon Ghouls, etc.
• Spells that target 'friendly' models (Healing Hand, Skitterleap, Hellish Vigor, etc) can be cast on anybody as long as they're a willing target. Decide this before dice are rolled to cast the spell. Spells that only work on a particular type/race of model are still limited to appropriate targets (ie Hellish Vigor can still only be cast on undead targets, etc).

Shooting:

• Normal rules apply (ie single man-sized models on foot are at -1 to hit, etc).
• Models may shoot into combat as long as no friendly models are involved. Hits are distributed as shooting hits (surpise surprise).

Combat:

• No challenges can be issued or acceped (even if you're a Blood Dragon or something and normally have to). This means that things like Van Horstman's Speculum/the Annoyance of Netlings/the Virtue of Confidence/etc won't work.
• If models from three or more sides are involved in one combat, all models are considered to be in base-to-base contact and are therefore able to all strike each other.
• Combat resolution: After each side involved in the combat has worked out their attacks, work out each side's combat resolution score. To count as outnumbering, a side must outnumber all enemy models taken together (ie a US2 model on a horse does not outnumber two US1 models, even if they're not on the same side). The side with the highest CR win the combat; all remaining sides lose combat by the difference between the winner's CR and their own CR. For example: Model A causes no wounds, model B causes 1 wound and model C causes 2 wounds and is riding a dragon (and so outnumbers the other two combined). Model A has CR 0, model B has CR 1 and model C has CR 3. Model C wins the combat, model A loses by 3 and model B loses by 2.
• If all losing models flee from combat, the winner may choose to pursue any one of them. If any models do not flee, the winner cannot pursue and must stay to fight them.
• Models will only autobreak from combat due to Fear if the winning side has the outnumber bonus as described above.

Rationale Behind Things

• Rolling randomly to see who starts each round of turns mixes things up a bit and makes things less predictable. (Could probably change this to just continually going around the circle, though? Would be slightly simpler.)
• Slowing down fliers in the passages was intended to make it harder to create characters that were impossible to catch. This would mainly be a problem with mages and characters with nasty missile attacks.
• Limiting spells to LoS means that you can't hide a couple of Goblin Great Shamans/Heavens mages/etc in a corner somewhere and try to stomp/zap/etc everything to death.
• The rules for dispelling are basically to make sure that people can't sleazily 'throw' dispel attempts by making a pathetically weak attempt (ie 1d6 vs a spell cast on a 14). The limits on dispelling Remains in Play spells are to ensure they actually get to stick around and do something - it'd otherwise be too easy to get rid of them as players would get so many attempts.
• Getting rid of challenges means that 3+-way combats aren't interrupted by two combatatants becoming suddenly untouchable by the rest and means that chariots are actually vulnerable in one-on-one combats. It also gets rid of magic items that would otherwise be a bit good (read: total no-brainers) in a situation where the vast majority of things you'll fight are characters.
• Allowing everybody in a multiple combat to fight each other means that you don't get the strange situation of a character charging into an existing two-way combat, slaughtering one of the fighters and then beating the other without giving them a chance to strike back. If everybody gets to fight everybody else, applying the combat resolution to everybody seems a lot fairer.
• Basing outnumbering off the total number of enemy you're fighting seems a bit more logical than one model on a horse outnumbering 8 seperate enemy models on foot. It also makes autobreaking things a bit harder in multiple combats unless you've brought a proper monster rather than just a bony horse.