So I have been reading all about how Mutas are very difficult to deal with in PvZ and in some cases people have said that Protoss simply cannot fight Mutas right now and something needs to be changed. Well I have a couple unit combination's that I've tested vs Mass Mutas, Muta/Ling, and Muta Hydra. I will start with units that don't work vs Mutas.
Pheonix - For some reason the Phoenix dies in a split second vs Mutas even in large numbers. I think Blizzard intended the Phoenix to follow in the foot steps of the sair as a harassment unit. It works well for sniping lone overlords but pales in comparison to sairs when it comes to fighting groups of air units because splash is non - existant.
Stalkers - I attempted massing stalkers vs Mutas and the results were always the same. 40 stalkers vs 32 mutas = mutas win. 40 stalker vs 28 Muta = mutas winn but it was close. If zerg even adds any lings to the mix you just won't stand a chance.
Archons - Archons are actually great vs mutas except for zerg can get SOOOO many mutas and with the amount of pressure on your gas all game there is no way to make enough archons alone to deal with mutas. Mutas also do not stack like before so the splash is not as effective.
Void Rays - Well they only attack one unit at a time and for a pretty long time. Against a large number of Mutas they stand no chance.
So after all the tests and all the failures I had. I began to think, wow people are right. There is just no way for Protoss to deal with mutas. Even after knowing they are coming and having plenty of time to prepare a muta-ling army would roll me so fast. So I searched the Tech-Tree in the help menu and found something really surprising to me. That cute lil snow globe they call the 'sentry' in the stats has a green box that says, "Strong Against, Mutalisk". I thought WHAT?! This thing has 40 HP and 40 Shields... I don't even think it could beat an SCV 1 on 1. So I gave it a whirl. Here are my tests results.
12 Muta vs 9 Sentry = SENTRY WIN! (I know shocking)
24 Muta vs 18 Sentry = Sentry win.
So I realized I don't even need to have as many sentry as they have mutas to stop the mutas. Every test I did of course was while using the Sentry's force field ability that reduces ranged damage by 2. This cuts down the initial blow of the muta from 9 to 7, then the second shot from 3 to 1 and the last shot still doing 1 damage. So after all this I thought okay realistically Zerg will not just have only mutas. So I tested against Muta/Ling and with sentry alone of course they lost. However, when I mixed 10 zeals + 2 collosus + 12 sentry vs 12 muta and 36 lings, I won with NO problem at all. Collosus kill all the lings while the zeals take the damage, the mutas target the sentry where the sentry always win vs muta in close numbers. I then proceded to try different combinations of units along with the sentry and the safest combination felt like it was collosus + Zeal + sentry, and if you can afford it or have teched to it making templar for storm to help cast on the muta will tip things so far in your favor a counter attack would most likely win the game after the big fight. So those are my findings. Now I am usually playing Zerg on the ladder so if you see me in a game well... ignore what I said here and just try to go collosus on me while I muta ^.^
Just for those who don't have a beta yet and are curious. Money wise it is completely affordable to mass up on Sentry as long as you have both your double gas. Zerg will also need both double gas to support his mutas. Muta cost 100 mins and 100 gas. The sentry cost 50 Mins and 100 gas. This will give you extra minerals to spend on zealots/pylons/gates/ and still have enough to mix in some stalkers and collosus.
Summary. Sentry needs to be at about a 3/4 ratio vs Muta if you want to trade armies and possibly come out on top with 1-2 sentry's left. Your safest bet of course is having 3/4 ratio of Sentry/Muta and also having support by a couple stalkers, templar, and/or archons. Having your zealots around ur sentry also help to pick up some of the bounce damage from the Mutas as well so keep that in mind.
P.S. Sorry if this post was extra long but I just wanted to make it clear how everything worked out for me.
I am open to any feedback if you guys have any! Let me know your thoughts and opinions and if you know of any good builds to get your sentry army up and running. I only tested the unit combos themselves, I haven't tested any specific precise build orders to fight vs mutas. I just know the goal is to get sentrys mixed in with my army and to try not to fall behind in the Sentry vs Muta count or it could be devastating.
Edit -Grammar/Spelling/minor sentence structure. (also it was 18 sentry vs 24 muta not 16)