Monster Mash!

Double post day! I wanted to post a list I found interesting that combines Daemons and CSM and MONSTERS!

Your opponents after you set down your army

The army list is thus

HQ
Bloodthirster
Keeper of Secrets (Why? The MoS DP unlock.)
CSM Daemon Prince

Troops
10 Chaos Space Marines
10 Chaos Space Marines
10 Plaguebearers
10 Plaguebearers

Elite
Mutilators (They do have a use!)

Fast Attack
Heldrake

Heavy Support
3 Daemon Princes

Total without upgrades: 1605

I enjoy the 1999+1 style games so in that case there'll be 395 points of upgrades left. I'm not sure I can get that high so some units will be really decked out. I'll discuss now what upgrades I chose and why and give you an idea of how to tailor your list to emulate your local meta-game and unleash the flying monster circus.

HQ
Bloodthirster
Bust open some tanks and put the hurtin' on back-line heavy weapons and dedicated CC units. Bloodthirsters fall easily to tarpits and massed fire so you want to maximize his potential as a flyer and as an assaulter. I give him a Greater Gift and a Lesser Gift. With Greater gift any roll is good except for 6 in which case trade-up for a Greater Etherblade. With Lesser Gift you can take pretty much any and be fine. If he won't be in reserve trade away Warp Strider for an Etherblade (giving you a bonus attack and master-crafted).
Total: 280

Keeper of Secrets
For the Psyker level always roll on Excess. Any of the three are awesome and it may be worth it to buy a second Psyker level for a dip into telepathy (you reaaaaally want Invisiblity) but in my case I'll buy the beast a Greater Gift and take a Lash of Despair (if not any of the others). No need to pump points into a unit that'll probably die within a turn or 2 to shooting.
Total: 190

CSM Daemon Prince
This guy (and the other DPs) should be decked out. I'll do a Mark of Tzeentch for added survivability and wings to make it a flyer. We don't really need weapons (artifacts are pricey and don't add much killy) but a Gift of Mutation is definitely warranted (Especially since you can't be Spawned or Dark Apotheosis'd).
Total: 210

Troops
Chaos Space Marines
10 troops so you get the second special weapon. In total you have very few troops which is a problem but the list's goal is to wipe out threats to the troops while keeping them back away from but dangerous for light vehicles and back-line harassers. Honestly you could give them flamers and Mark of Nurgle to make them true campers and switch out all of the bolters for CC weapons and engage those who get close. I'd let the sarge remain un-upgraded but splurging on a power sword isn't a bad option.
Total: 170 [340] (I just bought 2 plasma guns and 5 extra men)

Plaguebearers
Sit down and attempt to put your fist into your mouth while you wile away the time. You are a plaguebearer, there's nothing fascinating in your basic stratagem but you can now slap vehicles big and small to death, which is great, and you can wound everyone always. The new poisoned rules mean you'll be re-rolling your beatsticks against T3 or lower (watch out FX) but everyone will still get their armor saves but who cares. They're the best tarpit in the business for the points and need no upgrades to be dangerous.
Total: 90 [180]

Elites
Mutilators
Why mutilators? How can you even get them into CC for them to survive? The point is thus: your opponent has to either shoot at the Mutilators or shoot at your Monsters. I know of few armies that can shoot at all of them and fewer still that don't worry about getting engaged in CC by them so the Mutilators point is two-fold: 1. Kill enemies 2. Absorb fire. To do both of these I'd take them with MoN and walk them up the field. A wall of ominous portent indeed.
Total: 165

Fast Attack
Heldrake
It's the scare unit of CSM. The torrent flame weapon mops up MEQ and FX squads like nothing. They pull down enemy flyers and slice open lighter vehicles like they're paper. The Hades Autocannon is pretty great as well against FX and some vehicles (even better with Daemonforge). An obvious take.
Total: 170

Heavy Support
Slaaneshi Flying Daemon Princes
Why did I get 3 Slaaneshi Princes? Lash of Despair. This Greater Reward gives you 2d6 S6 AP- attacks. Enough to bring down any vehicle less than a Land Raider and with Vector Strike you can smack the crap out of blob squads and the enemy back-line. They'll all have wings as well obviously. Also, a little obviously again, they'll have Psyker levels. One or two, up to your personal taste but I'd do 2. One Biomancy power and one from Excess (never Primaris, roll).
Total: 265 [795]

Conclusion
Now the total I got for this whole shebang is 1998. It's a bit scatter-shot I'll admit but you're so dangerous in CC and still have shooting (in a Daemon list!) that you are dangerous all over the place and have 5 extremely mobile units to play with. The Lashes together get you 6d6 S6 shots per turn (potentially very deadly with an average of 21 shots per turn) and most of your flying units can practically ignore anti-flyer shooting. The Slaaneshi psychic powers can blow away blobs or prevent back-line heavies from shooting (You'll scream, 'Get pinned!' more than once) or stop an enemy from attacking or shooting you back when you charge them (honestly, what does 0 initiative mean? I say it means no attacks back).

Your army is extremely mobile, very survivable and can slap down a ton of very deadly anti-vehicle anti-infantry attacks. You're a flying mailed fist. Your problem may become other flyers or back-line killers wiping out your undeveloped troops. Really though, I like the list and have a lot of fun with 6 MCs that aren't Tyranids.