Screamerstar is the new overnight sensation for daemon armies. It features one or more Screamer units - one of which at any time can be buffed to a 2++ re-rollable invulnerable save (Tzeentch daemons always reroll a failed save of 1). Screamers are highly mobile, multi-wound, have a S5 AP2 melee attack (Lamphrey's Bite) plus they can Slash attack. The army revolves around the Screamers, Kairos the Fateweaver (aka Big Bird), another unit that has the Grimoire of True Names (GoTN) and several psychic level 3 Tzeentch Heralds casting from the Divination psychic lore. If a Herald should roll for Forewarning (blessing) it can give a friendly unit a 4++ invulnerable save. The unit with the GoTN then converts the invulnerable save to a 2++ and the Fateweaver allows the daemon player to re-roll for the Grimoire to better ensure the 2++. So there are several factors which must all occur every turn in order for the crazy buff. By eliminating just one of these factors you have greatly diminished the daemon army's central most strength.
A 2++ re-rollable save is nothing new... Dark eldar|eldar armies used this tactic towards the beginning of sixth edition. The major difference now is that instead of one character tanking wounds for its entire unit, all of the Screamers in the recipient unit have the 2++ re-rollable save so the daemons are much more resilient and not susceptible to counter tactics such as barrage sniping.
There is some controversy whether or not the S5 AP2 melee attack benefits from the +1 attack when charging. By a pure RAW interpretation it's only a single attack. Another controversy is whether or not Fateweaver allows the re-roll while held in reserve. Finally I believe that for a Slash attack to work the Screamers must completely pass over the target unit. It all depends upon the TO's call in a tournament - you can always ask ahead of time to make sure and not every TO will rule in favor of the daemons - it's definitely worth asking!
Screamerstar can feature four Tzeentch Heralds in the unit... One carries the Grimoire, one casts Forewarning, one casts Prescience and every other warp charge point goes into Flickering Fire (S6), averaging over 40 hits a turn. This combination is highly dependent upon the Heralds rolling for the correct powers, which can be a weakness to this method.
Sample Army List
Herald of Tzeentch on Disk Grimoire
(Perfect Timing, Prescience, Flickering Fire)
Herald of Tzeentch on Disk Portalglyth
(Prescience, Forewarning, FF)
Herald of Tzeentch on Disc Locus
(Precognition, Prescience, FF)
Herald of Tzeentch on Disk
(Scryer's Gaze, Prescience, FF)
Flesh Hounds x10
Daemon Prince of Tzeentch
Wings, Armour, Greater x2. Lesser
(Hellfire Gaze, Daemonic Resilience, Staff)
The key to beating this army are as follows:
1) As always first and foremost play to the mission objectives. Don't immediately start the game all flustered and try to be the man going after those nigh invincible Screamers... Sure the Screamers will be up in your face as fast as the daemon player can get them there but if your army is mobile and|or has many units there's only so much damage those Screamers can do. Contain them at arm's length when possible and throw speed bumps in their path to slow them down.
2) Focus on destroying either the Fateweaver or the unit with GoTN. Once you have destroyed either of these two units the Screamers are then much more manageable. While the Fateweaver is very resilient there are certain armies that have the right tools to quickly and efficiently shoot down Big Bird - Necron armies with lots of Night Scythes and eldar armies with lots of Wave Serpents both immediately come to mind. Tau can dedicate seeker missiles if necessary. Big Bird doesn't like any flakk either (no pun intended).
If you focus a lot of fire power on Kairos another advantage it is more likely the daemon player will have to use its re-roll to protects their precious Big Bird. If Fateweaver is held in reserve then first focus on destroying the unit with the GoTN.
This strategy puts the daemon player on their back foot forcing them to play more defensively thus blunting some of their offensive strength. If you can dictate the course of the game then you're much more highly likely to win.
You can also focus on destroying the Herald casting Forewarning as well. There could be multiple Heralds casting this psychic power - it's best to focus on first removing one element that will stay gone. The unit casting Forewarning must be within 12" of the recipient Screamers so it's not all that easy for the daemon player to hide... Sometimes they will be the easiest unit to reach out and hurt.
3) Don't play to the daemon army's strengths. You can waste a lot of fire power trying to shoot down a multi-wound unit with a 2++ re-rollable invulnerable save. You might be able to tie them down for awhile in close combat but still you're not going to put a serious dent into those Screamers.
4) One major weakness of Screamerstar is typically the Screamers are not a scoring unit. This is an advantage for you in any mission that features multiple objective markers. Of course if the mission is The Scouring then you'll have to take it on the chin but that should be only one in every six missions.
5) Certain armies have really good tools to quickly banish the Screamers and|or limit the psychic capabilities of the daemon army. Space Wolves have access to the Rune Priest - his rune staff blocks any enemy psychic power on the roll of a 4+ within 24" and Jaws of the World Wolf can make those Screamers disappear really quick. Tyranids can use their Shadows in the Warp to greatly diminish the daemons' psychic powers and this is very easy to do with winged Hive Tyrants. Drop pods can easily deliver units to target the daemon unit with GoTN - it's well worth sacrificing one unit early in order to eliminate this key.
I have provided simple guidelines how to beat the Screamerstar. Just like any other army it has its inherent weaknesses which you must exploit to win. The main key to victory is destroying the units buffing the Screamers, not the Screamers. Three things must happen each turn in order for the Screamers to have a re-rollable 2++ save. Focus on whichever of these three (i.e., Fateweaver, unit with GoTN or the Herald casting Forewarning) is the easiest to eliminate first. Do not play to the strengths of the daemon army or you'll most surely lose. Certain armies such as Space Wolves and Tyranids have in-built natural counters to Screamerstar... Use these to your advantage. As always play to the mission objectives and the inherent strengths of your army. If you follow this advice you'll soon be well upon your way to a decisive victory versus Screamerstar.