Hordes from the North
Defenders are regular Dark Elves with slight modification to the list, while the attackers may be Cult of Slaanesh, Chaos or Orcs and Goblins.
Overwiev
The Cult of Slaanesh and with them the Hordes - be it green or black - storm against the Druchii border defense.
If they manage to break through there way is open to attack the cities of Ghrond, Har Ganeth and even Naggarond itself.
However, if they hesitate the defenders get powerfull reinforcements.
Armies
Both armies are chosen to an agreed points value.
The defender may take one unit of witch elves or executioners as core choice for each available lord slot. These units count against minimum core choices needed but don't use up the lord slot.
This reflects how the Temple of Khaine helps to defend the borders against the enemy.
Battlefield
http://www.druchii.net/album_page.php?pic_id=1192
Place northern wastes terrain.
The defender gets one watchtower for each full 1000 points of agreed army value. (3000 points defender will have 3 watchtowers.)
Deployment
The attacker now may decide to keep up to one half of his units in reserve. They will enter the battlefield over his own long table edge in the first turn (stupid units in reserve count as passing their stupidity test during the first turn).
Both sides roll a d6 to decide who sets his first unit. After that players deploy their units alternating.
The defender's RBTs (if any) are deployed at the same time thought they may be placed in different parts of the battlefield. They may also be placed on top of a watchtower (max one RBT per tower).
Champions are deployed with their unit, all other characters in the army are deployed after all other units, all at the same time.
The defender may deploy scouts (anywhere on the table) after all other units are placed. They may not be deployed closer than 12'' of the attacker's units.
Scouts of the attacker will have to be deployed with the rest of his army but may make one free move before the game starts.
Who goes first?
Both sides roll a d6. The attacker adds +1 to his roll. The player with the highest result decides who goes first.
Length of game
Roll a d6 at the end of the sixth turn. On a 4+ another turn for both sides is fought.
The game will also end if one player gives up.
Special rules
Units of the attackers may decide to charge a watchtower as a normal target (frenzied units don't have to!).
They may decide to either capture or destroy the tower once they are in "close combat".
Only infantry units may try to capture a tower.
To capture a tower the unit has to remain in contact with the tower until the following combat turn (enemy's turn). The unit counts as a normal target until then (can be charged and be shot at). They will climb the tower after that turn and reach the top at the beginning of their own following combat phase.
If there is a RBT on top they count as charging it and will have to fight it. The attacking unit will not get any rank bonus but the RBT gets a defending bonus of +3. Should the attacking unit win the fight and the RBT's crew is killed or flees (killed automatically) the attackers capture the tower. If there is no RBT on top the attackers capture the tower without a fight.
A captured RBT may be used by assigning two warriors (and only DE warriors!) from an attacking unit as crew.
To destroy a tower the unit will have to tear it down. The tower counts as having 6 wounds on toughness 8 and is immune to poison attacks. It's also "unshakable".
RBTs on watchtowers may only be charged by flying units or under the conditions of capturing the tower.
Note: Chaos or Orcs and Goblins may not use captured RBTs!
Victory conditions
Count victory points ignoring table quarters.
The attacker gains +200 victory points for each captured or destroyed watchtower.
The attacker gains +100 victory points for each of his own units in the victory zone, not counting characters and monsters.
The defender gains +200 victory points for each watchtower still intact and not under attackers' control.
Aftermath
If the attackers win this scenario it may open new battlezones like Ghrond and Har Ganeth. To open battlezone at Naggarond should require either a lot of massacres on the CoP side or another fight on the way to Naggarond.
If the border remains defended it may open just the Ghrond battlezone (for larger battles) and probably one battlezone in the mountains between the watchtowers and Har Ganeth.
Note: I intended to make it easier for the attacker to achieve a victory than for the defender. This is for story purposes only. If you disagree feel free to reduce the bonus victory points for the attacker/defender accordingly.