The temporary twilight Kin list has now officially been made available on Mantic site, they added chariots units and hydra compared to the last beta version :
http://www.manticgames.com/free-rules.htmlNote that it is temporary because they plan to redo completly the army in a later supplement to make it more distinct from the other elves.
I will start with the easy matches :
-units---------------------------
Dreadspear => Spearmen
Darkshards => Crossbowmen
Witch elves => Blade dancers
Sisters of slaughter => Blade dancers
Corsairs with two weapons => Blade dancers (if you don't want to use witch elves, else mix them with the hand crossbows)
Corsairs with hand crossbows => Buccaneers (you can mix the unit with some models with two weapons if you want)
Shades => Shadows
Black Guard => Reaper Guard
Executioners => Reaper Guard
Harpies => Gargoyles
Cold ones knights => Dark knights
Dark Riders => Heralds of Woe
Chariots (both types) => use several as a Darkscythes Chariots unit
Reaper Bolt Thrower => Twilight Bolt Thrower
War Hydra => Hydra
Kharibdyss => Hydra
-characters---------------------------
Dreadlord/noble => Dark lord or Dark avenger (the Dark lord has an inspiring aura, the dark avenger does not and is only a pure fighter), note the options for cavalry mount (horse/cold one), pegasus and dragon (dark lord only for the dragon)
Sorceress => High prietess of the Abyss
Banner bearer => Army standard bearer (inspiring but weak in combat, note that you can have multiples)
Assassin => Twilight assassin
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Now this leave the following units without a direct equivalent
Bleakswords
Doomfire Warlocks
Cauldron of Blood
Bloodwrack shrine
Medusa on foot
The medusa can be simply used as a High prietess, just give it different spells that any other caster to make it more distinct.
I would probably merge the cauldron of blood or the shrine with an unit of Bleakswords and use them as a lower abyssal units, the cauldron/shrine serving as the fluf reason for the unit having regeneration.
If the lack of the racial Vicious rule bother you, note that there is a 25 points artegact that can be equipped to the unit to git this rule.
Alternatively, if you want to keep the khainite theme of the cauldron, then you might use the same idea with executionners instead and use the lower abyssals with great weapons variant (and/or give the brew of strength to the unit)
For the warlocks, one solution is to use them as Heralds of woe, their spells being represented by the ranged attack, with maybe one artefact to make them more distinct from the normal heralds, maybe one that give a small bonus to their ranged attacks for exemple.
Alternatively, if you want to keep their original magicial defense theme, they might be used as Dark knights with the Diadem of firekin (give a breath attack to the unit)
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From the Kings of War side we have the following units with no direct equivalent :
Lower abyssals => see above for one possible use
Twilight Dragon Breath => occasion to convert your own war machine, or maybe use somthing like the lizardmen salamander with dark elves handlers from the war hydra kit ?
Abyssals Riders => Monstruous cavalry, good occasion to convert or kitbashsomething. This might also be used to represent some kind of fast monstruous infantry/beast as long as the unit footprint matches.
Dark avenger on abyssal mount => Hero version of the abyssal riders, might maybe be used for a lone cold one chariot
Archfiend of the Abyss => Perfect for an Avatar of Khaine, using the statue from the cauldron or the Forge world model
Ba'su'su the Vile (special character) => Harpie special character, give option for an upgraded harpies unit.
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If you read everything I wrote you will have noted note that artefacts can be equipped on normal units and not only on heroes, this is a great boon for customization, and can help give reason to use some models.
For exemple you might want to use your sisters of slaughter as blade dancers, but what if you already use witch elves as blade dancers too ? You might use both units with the same profile, but you might also use this occasion to use one of them (or both) as an unit of blade dancers with a magic artefact.
Another exemple would be the black guard and the executionners. I recommanded both as Reaper guard (unless of course you use the executionners as lower abyssals with great weapons), but one way to differentiate the two units might be to give the executionners the brew of strength (improve crushing strength by 1 so they would get a powerful CS(2)) while the black guard might get the blessings of the gods (give the Elite rule so they would reroll both the 1s on to hit roll( elite) and on damage roll (Vicious), making them even more reliable)