This is meant as a tactical discussion on alpha strike based armies, both tactics for use by alpha strike armies and tactics to use against alpha strike armies.
I believe this topic is of greater importance than ever before in the game. These most recent codex lists have been mostly armies which are very high damage output but either low in model numbers and/or low defenses. Examples of these are
CWE, Skitarii, and the new War Convocation formation. Each of these armies can alpha strike an unprepared force nearly off the table in 1-2 turns but when they fight each other the roll for turn 1 or a seize the initiative roll can win the game. For the purposes of discussion let's look at some of the army lists I have seen used lately on frontlinegaming batreps as they are easy to find and pull and I like Reece and Frankie and their antics, plus you can read or watch them in use if you want.
Skitarii War Convocation vs. Eldar As you can see all of these armies have an absolutely brutal alpha strike. In fact if both armies deploys and one army shoots first the other army will lose 50%+ of their entire army on turn 1. This is because all three armies share some key factors; 1) fragile, 2) extreme damage output, and 3) synergy. On fact these armies can and will kill most armies in the game with their alpha strike and leave unprepared players shaking their heads in frustration as they pick models off the board. However this was not a predestined outcome all of that woe could have been avoided if the person going second uses the appropriate strategies and includes the tools they need to survive. It is much like taking units to deal with DSing scorers and taking anti tank. Extreme alpha strikes have become a strategy that needs to be considered not just during deployment but even in the list building stage.
BTW one mistake I have seen a lot of so far is with Canticles of the Omnissiah. People have been completely ignoring the underlined portions and thus taking the highest benefit from the canticles where they should not.
the strength of each Canticle will vary according to the number of units performing it. At the start of your turn, add up the number of friendly units on the battlefield that have the Canticles of the Omnissiah special rule and apply the appropriate level of effect. Do not include units that are currently Falling Back in this total.
This is making the rule ridiculously broken in several of the games I have seen. For example Reece deployed his destroyers in drop pods then claimed the max benefit from his canticle turn 1 when he had only had 4 qualified units on the battlefield at the start of his turn. This is the cost of using reserves with this formation. (just a specific example, the war convocation is ridiculously hard to remember all the rules for)
With such extreme armies how do you deal with not going first or how do you survive not bringing one of these above lists? The key word is planning, ie bring the tools you need. These tools should be some combination of; 1) extreme durability, 2) fight from reserves, 3) out of range/
LoS, or 4) ensure turn 1.
1) Extreme Durability IMO this is best demonstrated by the typical nids flyrant builds. The basic strategy is to start the game and take turn 1 or seize the initiative alpha strikes on a 2+ cover save usually from a source of shrouding and ruins/fortifications. They then have their flyrants go into swooping where they become extremely durable even without the higher cover save. This strategy needs fixing against the three armies above as each army has a way to kill the malanthrope, reduce cover save, and/or shoot flyrants out despite the 2+ cover save. However other armies can successfully implement this strategy.
IG is one of those that can use a version of extreme durability even against the three lists above. How they do this is with artillery units behind an
ADL and the order get back into the fight to let the artillery fire turn 1. This usually equates to 20+ wounds of T7 Sv2+ that the opponent has to deal with to meaningfully reduce the return firepower.
Interestingly enough the War Convocation can also perform a version of this centered around an
ADL and using Incantation of the Iron Soul to gain fearless to pop their
GtG units back up to shoot normally (or take the snap fire BS2 relic and just stay
GtG against a flyrant based list,

).
2) Fight from Reserves The skitarii list starts in drop pods so they have actually planned for this in their list building stage. The other two lists give this a nod with the war convocation starting some of their stuff in pods and the
CWE list including an autarch to help with reserves rolls however this strategy is not nearly so polished in either of those lists as the skitarii one which can happily fight going first or second and only cares about the roll for objective scoring and psychic buffs purposes.
IMO if you cannot execute an extreme durability strategy turn 1 then you should plan to fight from reserves in the list building stages. This means either almost entirely basing your army in drop pods or turn 1
DS abilities/units or bringing cheap durable units to hold turn 1 and reserves manipulation to bring units on en mass on turn 2. For example below is the
CWE list I use for max challenge games. Note it is very similar to Frankie's above but I have incorporated fighting from reserves considerably more in the list building phase by including cheap disposable units to take the turn 1 abuse rather than hoping not to be tabled or having to depend on an expensive wraithknight to take the abuse turn 1 like I have seen numerous players do. Imagine if when Frankie's D-Scythe wraithguard came down they could have exited a transport and thus spread out and caught the 3 units Reece bunched up like Frankie wanted to do but couldn't because he had to use his transport to help survive turn 1.
BTW the extra scatbikes could be included in my list at the cost of the seer council having actual offensive kick. My seer council can shred units with
Ld based attacks whereas without the armour of misery and Iryllith the seer council is a distraction unit.
You can see that 160 pts (2 scatbike units of 3) bought me the ability to fight significantly more effectively out of reserves than a list without a couple of T7, 4 wounds artillery units and an autarch could ever hope to. The best part is that the shadow weaver artillery are still fairly effective dakka.
Most of the competitive lists I design now fight out of reserves effectively or are based around extreme durability.
IMO a list that doesn't incorporate some element of these strategies will struggle against the new wave of top tier armies.
3) Out of range/LoS This is part strategy, part board dependent, and partially list dependent. How this works is to simply deploy your units out of
LoS and range from the majority of the opponent's firepower. This works best when combine with one of the other strategies and as it is usually impossible to completely deploy out of range or
LoS or all of the opponent's firepower. However against the war convocation this can be extreme effective as their isn't enough points to allow them to fight from drop pods and there are several disadvantages to doing so. Even against the drop pod and
CWE lists however deploying your units in the correct positions can significantly limit incoming firepower and even make the units come closer to you than they would otherwise want to do. These positions are usually the rear corners of your deployment zone and in the center of large buildings. This is usually dependent on the board layout and terrain however there are list building concerns which can enable this stratagem.
For the list portion you want units that are barrage and 48"+ ranges if possible. IME the Renegades and Heretics Ordnance Tyrant based list can if supplemented with good mobile scoring units make a very effective version of this list.
IG also do this very well as both can bring a variety of long range barrage weapons. Alternatively 48" threat range units like scatbikes can do this well but will often time struggle to deploy in such a way as to fully utilize this strategy. Additional concerns during list building include taking servo skulls to block infiltrators and scouts which could otherwise close and limit your options turn 1, and taking a bunker and/or bastion to hide units behind (ala malanthrope in a nid army). Most extreme alpha strike armies suffer from needing
LoS and 2 of the 3 above depend significantly on short range units to deal a significant amount of their damage.
A good example of where this strategy could have made a huge difference is in
this recent batrep where a proper counter deployment by the white scars player could have left Reece with only 3-4 units in range to shoot (hard to tell in a vid batrep). Having the benefit of hindsight over the white scars player (who did really well considering he faced a complete unknown of an army) I would have prefered to take my licks and get into melee where I could hit and run out than come in piece meal and take 2 rounds of shooting on most of the units before they could contribute thanks to stealth+shrouding on the entire war convocation (that would be the major decider for me, something I might add the white scars player didn't know about when he chose to null deploy).
4) Ensure Turn 1 This is a false statement but you can certainly work towards it. Take units like assassins, coteaz, or mantis chapter tactics to get a reroll for seize the initiative. Don't take
LoW in an ITC event so you get a +1 to seize. If you have both of these bonuses then you have a better than 50% chance to seize the initiative and most opponent's will just let you go first to avoid setting up badly and getting seized on. Note the two non drop pod lists both had
LoWs so you would get a +1 to seize.
Finally as a side note against the drop pods you might want to look up common anti drop pod strategies which range from bubble wrap units (can be effective if done well against skitarii but is very hard to do) to interceptor units (coteaz doesn't work very well however Ahazra Redth has a warlord trait to give his unit intercept).
MSU dispersion is also a very nasty counter to drop pod based armies and in general works well against extreme firepower lists assuming you don't play a
KP mission
As for alpha strike based armies. Most of the above strategies are useful if an alpha strike army goes second however even if you get first a highly recommend taking a character like coteaz or mantis warriors to make the opponent reroll successful seize the initiative rolls. There is little worse than getting seized on as an alpha strike list deployed to alpha strike. Alternatively fighting out of reserves like the drop pod sitarii list is always very effective even if it tends to give somewhat less intense alpha strikes than the other two lists above.
Thanks to anyone who bothered to read until here

. Please add your thoughts on the tactics for and against alpha strike armies.