I'm kind of reluctant to do this post because I'm very concerned that GW is going to change everything in the next FAQ. But here goes.
Let's assume that GW has not made a colossal omission in the codex and that icons working even if they weren't on the table at the beginning of the turn is how they designed the army. This could all turn out to be a repeat of Look Out Sir where their playtesters turned out to be so unimaginative that they couldn't catch something that took me two days to figure out. Nevertheless, unless they errata the icon, this is how I'm going to approach the army because thems the rules, and everything that seemed hopelessly doomed to rush across the board with low toughness, low saves and no assault grenades, now seems to make sense when understood that it can be right up on the enemy with only one turn for them to react. But I have been wrong in divining GW's intentions before.
I've read a bunch of premature Daemon reviews around the internets and I've come to the conclusion that people haven't got it figured out yet, but the book has been out less than a week, so give them time. There are bunch of misconceptions about the army.
- It is not a horde army. 9 point troop models (who are really quite poor for the price) do not constitute a horde. Orks, IG and Nids are hordes. Dark Eldar is not a horde. Neither are Daemons.
- Everyone looks at the army as though it were just like every other army out there where you line up most of your force across from most of the other force and bash heads. If you do that, you will get shot up as you attempt to cross the table, and lose in assault when you get there with the survivors because they have no grenades.
- Daemonic assault is not gone. The entire army still deep strikes for a reason. Read again: THE ENTIRE ARMY STILL DEEP STRIKES FOR A REASON. Ignore it and you miss the whole point.
Here's the deal. The Daemon army is designed to work off the icon/instrument mechanic. Instruments increase your odds of getting more of your reserves all at once. Icons work the instant they hit the table, allowing you to deep strike those reserves with precision. Therefore Daemons are a reserve army.
You deploy half of your force--the half that is survivable and/or super fast--and reserve the heavy hitters. On the second turn, you bring as much of your strike force onto the table as you can using the army-wide deep strike mechanic. Once the first unit with an icon drops, the rest of the force comes in without having to risk mishaps. Further units deep striking with icons allow you to pick and choose where your stuff arrives. The opponent now has a single turn to deal with your forces before they hit their lines. Even Warp Quake isn't much defense against this as almost the entire army is fast enough to close the 12" gap.
Once you understand this, certain things about the army make a great deal of sense.
Beasts of Nurgle are there to countercharge any units trying to assault individual elements of your strike force before you're able to charge yourself. They are not there to sit back with your lines in case somebody comes charging you.
Flamers have weaker shooting because you can drop them with pinpoint accuracy, and still cause terrible damage to infantry.
Seeker Chariots, Blood Thrones, Skull Cannons and Burning Chariots are all incredibly easy to disable because the enemy is only going to get a single turn to do it.
Bloodcrushers lost their 3+ armor save because they would be too powerful otherwise. The army lost eternal warrior for the same reason.
Epidemius only affects a single unit now because it is much easier to get a killy Nurgle force into the opponent's face than it was.
The Masque is good because she drops in and makes one of your enemy's most valuable shooting threats BS1 (or WS1 if fighting an assault army), effectively removing one of the precious opportunities to deal with your army during that one turn they have. Yes, the Masque is good. If she were included as one of your four Herald choices, you would always want to take her.
Fiends have anti-psyker powers to help against Grey Knights, and because they can be dropped right next to them (barring warp quake). Their initiative-reducing power is designed to work with the Rapturous Standard that Daemonettes and Seekers carry so that even though you have no grenades, you will swing simultaneously against whatever you charge, and they will need 5's to hit you.
Flesh Hounds, Screamers and Flying Monstrous Creatures are designed to be deployed, rush up the battlefield, and alpha strike something Turn 2 to help soften up the enemy forces before their chance to hit your strike force. Just as Burning Chariots are designed to drop on the enemy flank and take lascannon shots at side armor before it can be taken out.
With comms relays and instruments, you can pretty much guarantee your entire reserve force will arrive Turn 2 (or at least the parts you want), with only the first deep strike entailing any sort of risk. As long as this is true, the consequences will never be the same! Think of all the possible army builds you have at your disposal.
For backfield scoring, you can use Plaguebearers with shrouded 2+ cover saves, or Horrors going to ground behind an Aegis with a 2+ rerollable thanks to Daemon of Tzeentch, or you can use Daemonettes as they are fast enough to get an Icon up the board and join the rest of your strike force once they drop.
Flesh Hounds and Screamers are both able to work in the deployed half of your army and push upfield quickly, and Nurgle Soul Grinders can sit back in cover with impunity.
Your deep strike element has even more options available to you, and the trick is figuring out how to make it as survivable and dangerous as possible.
What if they do nerf icons to be like all other teleport homers? All is not lost. You can still get an icon upfield quickly. As Bill Kim points out, Karanak lets Bloodcrushers scout, so you can get them 25-30" upfield by the start of Turn 2. Seeker, too can run D6+6" after a 12" move, and can be kept out of sight. It's just harder to keep them alive.
So, any unit reviews of the Daemon army you read that do not take the Daemon reserve mechanic into account aren't going to do you much good, because if you try to play this army like Tyranids or Orks, you won't have a whole lot of success.
Now you understand why I restored the original blog motto.