Infernal Tetrad 2000pts
COMBINED ARMS DETACHMENT
Bloodthirster of Insensate Rage with 2 Greater Rewards
Herald of Tzeentch with Mastery Level 3 and Paradox
Herald of Nurgle with the Doomsday Bell and Psyker Level 1
11 Pink Horrors
Daemon Prince of Khorne with Daemonic Flight, 2 Greater Rewards and the Armour of Scorn
Daemon Prince of Nurgle with Daemonic Flight, Mastery Level 3, Greater Reward and Exalted Reward
Daemon Prince of Tzeentch with Daemonic Flight, Mastery Level 3, 2 Greater Rewards and the Impossible Robe (Warlord)
Daemon Prince of Slaanesh with Daemonic Flight, Mastery Level 3, 2 Greater Rewards and Soulstealer
Guess what? It's a Flying Circus Summoning list!
Tzeentch Prince is the Warlord because being a T6 3++ re-rolling 1s FMC with piss-easy ways to get to a 2++ rerollable (+1 Invuln warlord trait or Cursed Earth or Grimoire), and the Tzeentch traits are all really good for the Tetrad (-1 WS and BS when attacking them? Zing! Cast on 3+? Zing! Ignore a Perils every turn? Zing! +1 Invuln? Zing! ML4? Zing!). He flies around and is a pain in the ass; if he gets to 2++ rerollable, he'll drop down and charge some fools. If not, he's pretty happy flying about the place Summoning things and making a nuisance of himself.
Khorne Prince is the beater, being essentially T7 3+ armour; he goes and kills fools all over the shop, mainly aiming for enemy Monstrous Creatures. I wanted to give him Deathdealer so he could go after GMCs, but the Armour of Scorn is too good and I thought up another solution to that in any case.
Nurgle Prince is support. He's got a 2+ Jink and the Grimoire, but is the worst in combat (as far as 'worst' applies to a WS9 I8 Str6 A5 Monstrous Creature) as he can't Sweep, so he relies on flying around the place trying to stay in cover and giving out the Grimoire; usually to the Bloodthirster, but whosoever needs it most in that turn.
Slaanesh Prince is kinda the scalpel; he's fast enough to go after the weak things, with a Run of between 5" and 15", so he'll tend to go and mow through Devastators, Lootas, Guardians etc. to maximise his chances of staying at full wounds with Soulstealer. He's the most fragile, so has to be the most careful and try to combine his pushes with a push from one of the nastier guys to draw some fire, and is the most likely of all of them to roll all of his powers on Telepathy to get that clutch Invisibility or Shrouding. Didn't give him any armour because I liked the idea that if I find myself in such a situation, the Slaanesh/Nurgle/Tzeentch Princes can all go in and thin out the Grav Cav while the Khorne bros sit back and crack cold ones until the battlefield's a little less dangerous for them.
Bloodthirster goes straight for the enemy super-heavy or nasty HQ or whatsoever they bring that requires 8 thrusts of his Colossal D. Gets the Grimoire or Invisibility because if he doesn't die, he's going to really ruin peoples' day. I'm not entirely sure if I want the I1 all-night D of the Insensate Rage or go to the I9 Unfettered Fury with Deathdealer for a quickie; if Invisibility or Grimoire is up, it doesn't really matter, but slipping your D into a Wraithknight before it can swing would be a night to remember.
The Tzeentch little daemons contingent hangs back on an objective, Going to Ground in terrain because they're only there to cast buffs and fuel the antics of the Tetrad anyway. If the Princes are really giving the enemy a hard time of it and there's appropriate midfield terrain the Horrors will move up to get some sick sick 5-dice guaranteed Summoning. I don't know if it's a really good choice, as they might end up too far away to do much of anything, but it's certainly worth checking out and the Paradox is too good not to include in some way.
The Nurgle daemons are there to hold objectives and make Psychic Shriek/Terrify even nastier. That's it.
The Tetrad will all follow the same kind of system for their powers; first, you roll on Malefic. If it's Cursed Earth or, depending on matchup, Sacrifice/Incursion, they keep it and roll again on Malefic; if it's not, they swap out for Summoning and move over to Telepathy. If they roll Hallucinate, Mental Fortitude, or in some situations Dominate, they swap out to Psychic Shriek and roll again to gun for Terrify/Shrouding/Invisibility/sometimes Dominate (Dominate, on the whole, isn't fantastic, but against an already average Leadership army it combos deliciously with the Doomsday Bell and even moreso with Terrify; Grav Centurions that have to make a Ld7 or 6 leadership check, or a Riptide that has to make a Ld7 check, just for the privilege of shooting is a way better protective buff than WC1 would have you believe). I might experiment further with that, as Biomancy is pretty horrifying on Daemon Princes (Iron Arm, Enfeeble, Life Leech, Warp Speed and Endurance are all golden; Enfeeble makes the Khorne Prince fairly insane as he instakills anything naturally T5 or under on the charge, can Smash T6 MCs to instakill them at I9, and can't be hurt at all by anything under Str6!).