just some random thoughts here and im not sure how to put them togethor, or if this would be considered over powered, or just out of place, but here goes: THIS WOULD BE MUCH BETTER IF NOT FOR ILLEGAL BB CODES:
charater/boss
Arthas the Lich King
http://www.hiveworkshop.com/forums/resource_images/6/icons_5390_btn.jpg (image wont show)
http://www.hiveworkshop.com/forums/icons-541/btnkingarthas-90626 <--icon found here-----(25.72kbs)
http://www.hiveworkshop.com/forums/resource_images/6/models_5499_screenshot_tnb.jpg(image wont show)
model above found http://www.hiveworkshop.com/forums/models-530/arthas-nerzhul-merge-lich-king-arthas-90625 <---there (395.18kbs)
Frostmourne
http://www.hiveworkshop.com/forums/resource_images/7/icons_6898_btn.jpg
--http://www.hiveworkshop.com/forums/icons-541/btnfrostmourneon-117781/?prev=search%3Dfrost%2520mourne%26r%3D20%26d%3Dlist%26page%3D2 <---icon here
alright theres the visuals (that didnt work) hehe
Character/Boss ability ideas:
1. Death Coil (normal warcarft3 one would be fine just modify it to stats or something)
2. Army of the dead:
summons X amount of Ghouls that are of a certain strength etc(units buffed based on a certain stat?).
3. Hunger of Frostmourne (passive) - attack speed or dmg?
4. Death Grip - pulls enemy to the deathknight doing X amound of dmg*(this ability is just a filler)
5. Ultimate: not entirely sure here but here is an idea:
Wrath of the Lich King- the souls of the dead trapped within frostmourne are released causing a massive explosion to all in an AOE around the character
if its a boss aswell, much more to toy with there as they are not limited to 4 spells
Weapon Ideas:
1. Kills increase dmgfor every X amount of kills increase the blade's damage a certain amount for however dark chaos sees fit..
2. PVP encouragerfor every X amount of enemy heroes defeated increase the blade's damage a certain amount.. " "
3. Weapon Spellusing counters for kills when the weilder gets X amount of kills, he can use a spell based on a certain stats etc to release captured souls so a similar etheral explosion
anyway thats basically the idea in a nut shell, not entirely sure what your planning dark chaos but i know there is an 8mb file limit and there are ways to optimize the map with jass coding etc (check out the hiveworkshop for help there)