I've received multiple requests for the ultimate Slaanesh army of all time. Ok, you pervs, here it is.
While I would consider most Slaanesh stuff good, but they all have basically the same role. They're mobile and good at getting the enemy out of place, weakening them, and setting them up for a hammer blow. Well, if all we have is Slaanesh units, there is no real hammer. The best you can do is the Keeper, but because it is your only real beefy unit, it will draw fire and get taken out. In a mixed army where you can fit in other good tough units like Crushers, Nurgle DPs and Grinders, the Keeper can do its job very well. In an army with majority T3 and 5++ saves, it will suck up stuff like lascannons, missile launchers, and melta while basic and high RoF weaponry is concentrated on the rest of the army. Making target priority easy for your opponent is a bad idea.
The other big problem is Daemonettes. Relative to other gods, Slaanesh brings the softest stuff. You need scoring units to hold objectives and not die, but Daemonettes really aren't suited to that role. They are decent for killing infantry and going into cover, but they are far from durable. In a Slaanesh army, you don't need Daemonettes at all. Infantry killing is part and parcel of the Slaanesh moniker. All you need are scoring bodies to hide in the trees, really. You need to pick 1 or 2 objectives to hold, commit your girls there, and then use your mobile units (everything else) to keep the enemy off of theirs and occupied enough that they can't kill your Daemonettes.
So, to make pure Slaanesh work, I think there are two real options. You can either go for a pink and squishy version of the monster mash with 2 Keepers and 3 DPs, which has problems as I put out before, or go for death by papercuts. 1 unit of Fiends isn't going to go on a rampage, but 3 of them and 4 chariots and 3 units of Seekers? Ouch.
So here's the first.
"Size Matters" 2000 points Mono Slaanesh
2x Keeper of Secrets - Unholy Might, Sopoforic Musk
3x 6 Fiends, Unholy Might
2x 10 Daemonettes
3x Daemon Prince - Mark of Slaanesh, Iron Hide, Pavane, Sopoforic Musk, Aura of Acquiescence
5 MCs with decent survivability (T6 4++ and T5 3+/5++), the requisite Fiends, and Daemonettes to cap objectives and not die. Keepers and DPs start slow, but with Pavane/Fleet they can close fast enough and once you start using H&R you'll be all over the board. Fiends are awesome, as always.
This one doesn't scale so well just because it's about the minimum you need to make it work. Any fewer Daemonettes and you run into big scoring problems, and any fewer MCs and they become too easy to drop. If you want to go smaller, you'll be breaking theme by including PBs and possibly Grinders or different DPs.
My preferred version focuses on tons of mobile, middle sized units to just flood the board in cheap rending attacks with cav movement and Hit & Run almost across the board.
"Well, that was fast" 2000 Mono Slaanesh
4x Herald of Slaanesh - Chariot, Unholy Might, Sopoforic Musk
3x Fiends - 6, 1w/ Unholy Might
4x 10 Daemonettes
3x 10 Seekers
Delicious spam. 10 cavalry units, 7 of which have Hit & Run. Fiends and Chariots are your heavier hitters, going after armor and units in the open or just ping ponging around. Seekers dive into cover and tear up infantry and MCs with an insane number of rending attacks. Daemonettes can actually support here, but should be objective grabbers first.
This one can actually scale too. 1850 is just losing a unit of Daemonettes or Seekers, and 1750 would be from losing either more Daemonettes (I wouldn't recommend going below 3 good size units) or Seekers.
So, that's my take on mono Slaanesh. I'll continue with single lists, but if people want a breakdown for each mono god style, I'd be happy to.