This is based upon a scenario we ran in a "Citadel" as described, though I've tweaked the rules a bit to account for some of the problems we ran into in actual play. Note that many of the "scenario rules" mentioned here overlap those of my Urban Scenarios article.
SUMMARY: Scenario for 3 or more players controlling Corporate forces which comprise a joint "Cartel" force, against the Dark Legion (jointly controlled by the players) in a Citadel.
FORCES: Each player controls a 500 point army (or 501, for those who insist on being allowed to go a point over...), selected from any one of the Corporations. Any force may include Doomtroopers of the appropriate Corporation -- These are purchased outside of the usual restrictions for units and individuals.
If you purchase Doomtroopers, they don't add to your total number of Individuals for purposes of adhering to the rule that you may not take more individuals than units. Neither do they count as a unit for purposes of allowing you to get more individuals. You just pay the points cost and use what's left over to build the rest of your army following the normal rules. (i.e. A force with 1 unit of troopers, 1 Captain and 1 Doomtrooper pair is acceptable. A force with just 1 Doomtrooper pair and 1 Captain is unacceptable.)
If anyone wishes to play Cartel, they will only have an army comprised of Agents and Special Agents, though they will not have the usual -4 to Initiative penalty, since they have no squabbling Corporations in their ranks. (All the squabbling Corporations are played by other players, and presumably we can simulate the resulting chaos by the fact that they're competing with each other.)
If anyone should play Brotherhood, then that should only be if all the other forces do not have any Brotherhood individuals in their forces (with the "Seconding" rule).
RESTRICTIONS ON FLIGHT/VEHICLES: Since this takes place inside a Citadel, certain units may be of limited usefulness. Rams Air Cavalry and other flying vehicles cannot maneuver within the Citadel. A Necromower may be employed, though, depending on your layout, it could well get stuck in certain areas, forcing the driver to go on foot (MV of 3, armed with his Violator, and he can't take the Charger with him.).
Flight via spells or natural abilities, or in the special case of Martian Banshee rocket packs, is still possible for the purpose of moving up vertical surfaces, etc. There is no "mid-air" level at which line of sight is possible past all obstacles. Any such models must end their turn on the "ground" (or some platform, etc.) They cannot remain "mid-air" at the end of their turn. [The purpose for this is to avoid problems with keeping track of what elevation a flying model is for purposes of determining line of sight on other players' turns.]
THE NECROMOWER: (I use these house rules in other scenarios as well.) The Hedgehog Necromower can be used in this scenario, though its usefulness may vary greatly depending upon how wide those corridors are! A Necromower CAN be driven up steps with the normal movement penalty. It still has no ability to cross walls, let alone to climb them (or ladders). To offset this problem, the Necromower driver may disembark from his vehicle.
Disembarking from the vehicle or re-entering it takes a single action, and may only be done while the Necromower is stationary -- in other words, after a "Stop" action has been made if it has spent any previous actions in movement. When exiting the vehicle, the driver may be placed anywhere in base contact with the vehicle -- and, when entering it, he must already be in base contact with the vehicle at any position to get in.
On foot, the Necromower driver has the same statistics, save for a MV of 3 and an Armor of 24. He CANNOT take the Charger with him, though you may choose to give him some hand-to-hand weapons to use while he is on foot. When using this house rule, assume that the Necromower driver automatically comes with a Clansman Claymore which is already figured into his cost. The +4 resistance to the Dark Symmetry only applies while he is wielding it -- i.e., when he is on foot, or should he be in close combat while in the vehicle.
Using this house rule also supercedes the rule that the Necromower cannot be engaged in close combat. It may now be engaged in close combat (and vice versa) if a Stop action has been used to make it stationary -- or if it has otherwise become stationary due to a collision, etc. The Necromower driver may make attacks with his Claymore against any model in base contact with the vehicle while stationary, but he cannot make sweep attacks from the Necromower.
The untended Necromower and its Charger cannot be used by any other model except for another Necromower driver. (This is on account of special protective mechanisms to avoid tampering ... and arbitrary rules-making on my part so I don't have to venture into the realm of figuring out whether people can use abandoned heavy weaponry!) While untended -- and ONLY while untended -- it can be sabotaged by any model in base contact who spends an action to do so. It can also be disabled by any area-effect attacks (shotgun, flamers, rockets, grenades, plasma ammo, etc.) which successfully defeat an Armor roll of 28. This does not apply while the Necromower driver is present and in the vehicle. (Don't worry about the logistics. This is an abstraction!)
DARK LEGION: To determine how many points the Dark Legion gets for its army, take the number of players divided in half, rounded up, then multiply that number by the amount of points you were allowing for each army. For example, if you have four Co rporate forces with 500 point armies in the game, then the Dark Legion gets a single army of 1000 points. (4 divided by 2 is 2, times 500 is 1000.) If you have three Corporate forces with 500 point armies in the game, you get the same amount, becau se you're rounding up. If you only have two Corporate forces with 500 points, then there would only be a 500 point force for the Dark Legion.
As for the composition, the easiest way to do this would be to just borrow a pre-made list from whomever in your group sometimes plays Dark Legion.
OBJECTIVE: The objective of each Corporation as part of this joint expedition is to destroy as many points' worth of Dark Legion models as possible, while losing as few of its own forces in the process, whether due to enemy or friendly fire. (More on this later.) The Corporations, while in rivalry with each other, cannot directly attack each other. They can, however, do things to hinder each others' progress without actually exchanging fire...
The scenario ends when the Dark Legion is eliminated, or when all Corporate forces have been eliminated or have left the board.
To determine the winner, each Corporate player should keep any Dark Legion models he has destroyed in a collection, then after the game calculate the points' worth of each destroyed model. This is his initial score. Then, he should calculate the points' worth of every model he has lost (due to routing, being killed, etc.) and subtract that from his initial score. The remainder is his total score. The person with the highest total score wins. If anybody should have a tie, then it's a tie. ( Natch.)
LAYOUT: The Citadel is represented by a large assortment of floor tiles which define the layout of the building. Basically, wherever there is a floor tile, there is floor. Wherever there is uncovered table, there is solid wall. Obstacles may be put on the floor tiles as well, providing cover, obstacles to move around, etc. If you have any catwalks or other three-dimensional structures, then the "wall" rule still applies -- Being on a high vantage point doesn't give you line of sight to the whole board. It is still obstructed by any uncovered part of the table. You could have a catwalk passing over a floor tile -- in which case someone on the catwalk could have line of sight to figures below in the floor, and vice versa.
Setup can be a cooperative or singular effort. The best layout would probably start with a large open area in the center, with tunnels "radiating" outward to all sides of the table. Try to make sure that there are several "entry points" (a floor tile touching the edge of the table) on each table side. Next, if you have enough floor tiles (from such games as Warhammer Quest, Advanced HeroQuest, Siege of the Citadel, etc.) you should try to have some connecting passages between the "hubs", to in the end make something very roughly resembling a "wheel" with hubs, spokes and rim. This gives everybody access to the Dark Legion in the center (and vice versa) without everybody being stuck in a "dead end" to start with.
DOORS: If you have something to represent them, doors should be placed here and there. A closed door takes one action to open. If a model passes through the door, he may, for free, close the door behind him as he goes through. Otherwise, it takes an action to close an open door.
If you want to make sure a door STAYS closed, you can smash the "control panel" on a door, forcing it to stay shut until someone blasts it open. If someone attacks a door, they do not have to roll to hit (unless using an explosive device -- in which case deviation still applies), and the door counts as having one Wound and an Armor of 30. Once a door is blasted open, it is open for the remainder of the game -- It cannot be closed again.
Dark Legion models have control of any door within line of sight. (This extends even to the lowly Legionnaires.) Without spending an action, they can open a door or close it, or even lock it or unlock it. (A locked door is pretty much the same to Corporate players as one with a blasted control panel -- It will have to be destroyed to open it, unless the Dark Legion model chooses to open it again.) If the doors come into play too much, you may have to use markers to represent the status of a door. (Advanced HeroQuest doors work nicely for this, since the doors can be removed from their hinges to represent blasting, and they can be opened or closed, too.)
TERRAIN RULES: Decorations on floor tiles don't count as terrain. Only actual 3-D-represented obstacles placed on the floor tiles should be considered as presenting any sort of obstruction.
For stairs, it costs half movement to go up, but normal movement to run down them. [Note that this differs from my rules for urban scenarios. Whichever way should work, so long as everybody has to follow the same rule.] For any walls or other obstacles to climb, a rule of thumb should be that for each inch of climbing, you need to spend an Action. If you cannot get up the surface and to a place where you can stand in a single turn, then the surface is effectively impassable.
Ladders allow a model to move up a vertical surface at his regular movement speed ... though applied vertically. (i.e., 3 inches of vertical wall would take 3 inches of MV to traverse...) Again, you must end your turn on a standing surface. We can 't have models hanging on ladders, after all! (Hopefully nobody will design a layout with more than 9 inches of ladder at a stretch...)
Corners can provide cover. If you are standing around a wall corner and have part of the wall between you and your attacker, you are counted as having hard cover so long as your base is in contact with the wall.
It is assumed that large creatures (Ezoghouls, Nepharites, Eradicator Deathdroids, etc.) can move through the passages and even the doorways, even though your doorway markers might not be all that wide. Keep in mind that the Dark Legion wouldn't design these Citadels to be too cramped so that their head honchos can't even move around in them! Assume that the ceiling is high enough that it will not obstruct line of sight to any area that is not already obstructed by an imposing wall. (i.e., if you're aiming at someone on a catwalk, you don't have to worry about there being a low-hanging part of the ceiling in your way.)
Large creatures can step over obstacles up to 1 inch tall without any penalty to movement, and can move up stairs at full speed. Creatures that are not humanoid (Ezoghouls and Eradicator Deathdroids) cannot climb ladders, though.
DEVIATION: When grenades and rocket launchers are involved, and they deviate, chances are pretty high of the deviation area ending up against a wall. The blast epicenter must be placed somewhere in a non-wall position with line of sight to the original target area AND TO THE ATTACKER. (After all, even if you miss, your rocket can't fly around corners!) If you should roll for deviation in a direction where you simply can't move the rocket because of an obstruction or because of loss of line of sight to the attacker, then -- uh oh! Looks like the blast still caught you anyway! (That's the breaks of getting caught in a small room with a large explosion...)
DEPLOYMENT: Each player rolls to see who gets to choose first. If you have up to four players (assuming you have a four-sided table), then each person picks a side. If you have more players than that, then each person picks an /entry point/ -- This would be a single floor tile which touches the edge of the table. In this case, they would have to deploy their forces in that tile or room, aside from the usual 12"/6" rules. During terrain setup, make sure there are plenty of entry points of approximately equal size. (Their distance from each other doesn't matter so much, since the Corporations aren't directly attacking each other.)
If you have more than three players, in order to determine order of play, try this method: The person with the highest roll goes first. The person with the second highest roll determines in which direction around the table the turn order will go.
Capitol, unfortunately, cannot use Airborne Deployment or Air Strikes. That's just the way it goes -- Their superiority is in the air, and this is a battle taking place in an enclosed building. [At least they still have Martian Banshees!] Their Free Marines, however, can be placed anywhere other than another player's deployment zone. In fact they (or any other units with this same ability) don't have to be placed until AFTER all the other Corporate units have been placed, and after the Dark Legion has been placed.
Go ahead and have everybody place their entire army in their deployment zone immediately. There shouldn't be any tactical advantage to waiting to see where your rivals will be placing their units, since nobody is shooting at each other, and nobody should have initial LOS to another's area anyway.
Next, you have to place the Dark Legion. Dice off to determine player order, and then each player places one unit or Individual anywhere on the table, though it may not start within LOS of any Corporate unit. All Dark Legion models start off Waiting. Those that may Hide may start as Hidden as well.
Once all Dark Legion units have been placed, if there are any Free Marines in play, then they may be placed anywhere but in a Corporate deployment zone.
PLAY: Once the game begins, dice off to determine play order, adding your Leadership and any modifiers as per usual. Then, dice off to see who will control the Dark Legion this turn. (Don't add Leadership or any modifiers to this roll. It's simply a case of "highest roll wins".)
Play progresses as normal except that for this turn the player who won control of the Dark Legion can choose to activate a Dark Legion unit OR one of his own units during his turn. (He's essentially got two armies under his command for this turn.) He controls the Dark Legion within some restrictions (and you may have to employ some majority rule when certain special cases arise in the middle of the game) -- Basically he should play the Dark Legion to destroy the Corporation, not to just roll over and play dead if his own forces happen to be present.
Most of this should be determined as a matter of "honor". He should play the Dark Legion to trounce any visible enemies, but he is perfectly free to choose to have the Dark Legion focus more on his rivals than himself for any given turn. What would be unacceptable would be to have the Dark Legion essentially stand and make themselves sitting ducks so he can move in and destroy them easily. (He could, of course, wait to activate a unit that poses a danger to him until HIS forces can act first.)
If any Dark Legion force is in LOS of any of his forces, then when that unit is activated it HAS to use all available actions to attack his forces. (If there are any Dark Legion models out of LOS but nearby, he's perfectly free to make them wander off and attack someone else instead.) Any Dark Legion unit activated cannot simply "waste" its actions. If it has actions left over and cannot move or shoot, it should at least Hide (if possible) and Wait.
If his models destroy any Dark Legion forces during a turn in which he controls the Dark Legion, set the models aside -- He does not get points for destroying them. He also doesn't gain any points for any Corporate forces destroyed by the Dark Legion. He still loses points for any of his models which are destroyed or routed, though.
Next turn, you'll roll again to see who controls the Dark Legion.
ELIMINATED PLAYERS: If at any point in the game a Corporate force is completely out of the action (whether destroyed, routed, or voluntarily leaving the table) then that player automatically has control of the Dark Legion, without rolling. If there come to be more than one player out of the action, then dice off between /them/.
LEAVING THE TABLE: Any Corporate force can leave the battle area by essentially walking off the table from any entry point on the table edge, whether in its initial deployment zone or not. Once a Corporate model has left the table, it is out of the game for the rest of the battle. It does not count as being "destroyed" or routed, so it will not count against the player's points total. The player can't lose the unit, but neither can that unit accomplish much for the rest of the battle.
RIVALRY: Corporate models cannot target each other specifically, though there are still ways they can hinder each other's progress or even "accidentally" take each other out. (You don't get points for this ... but it will affect a different player' s points total at the end of the game, hindering his chances of success and thus enhancing yours.) Sample ways are:
You can't /choose/ to miss with a grenade or rocket blast, unfortunately. That would be a little too obvious as an attempt to attack your comrades with the "deviation".
Unfortunately, the Art cannot be used to attack other models, even if it could be done surreptitiously. Anyone even endowed with those powers would have enough respect for the Art not to abuse it thusly. Also, you simply can't attack another model directly. The Dark Legion may provide an excuse for undertaking risky maneuvers (with the others taking the risk), but you can't out-and-out shoot or hack another Corporate model, period.
(Note: A "possessed" model, such as one dominated or corrupted by Semai, counts as a Dark Legion model while it's so controlled. Then, it's fair game to take it out! You do not, however, gain any victory points for doing so.)