What's the best counter for mass Mutalisks and Corruptors?
I'm playing Terran at the moment, but I guess this question should concentrate the answers for Protoss and Zerg as well.
There is no unit that will magically let you beat a Zerg air mix, even Thors fall to mass Muta with a little micro. Instead let's break down what there is and discuss possibilities:
One of the things you need to ask yourself is: Is he Corruptor heavy or Muta heavy? This question will influence the result. If he's Corruptor heavy you're going to want more of a ground response. If he's Muta heavy, you're going to want more of an air response. I'll break down units for you based on this decision.
This is usually an indication he's going Broodlords, so its not a bad idea to build some extra Thor/Phoenix/Corruptor
Against a Muta heavy force you're going to have more success with air to air as every air to air unit stomps on Muta (and breaks even with Corruptors). You're going to want to back this up with a mineral heavy ground force (Queen/Marine/Stalker).
Remember, if you see Muta/Corruptor you need to think "How can I use what I have?" NOT "What should I build?"
A standard troll response to this is "if you let them mass corruptors, you're doing it wrong".
Of course, we're not all experts (myself included), so it is not terribly unusual to find ourselves in these positions.
If I was Terran against mass Mutas and Corruptors, I would consider the following:
1) Vikings with a ground-based support unit. Marines and/or Thors. I don't recall off the top of my head if Thors do area affect on air - Blizzard went back and forth on that in the beta, and it is an upgrade in Single player, just don't recall for Multi in release. And remember to stim your marines!!
2) Lure into fortified positions of bunkers/turrets, while repairing w/ SCVs
3) Counter-attack their bases/expansion. You may end up doing a base-swap, but if your forces will die when confronting the force directly, it's better than losing outright.
Support units in either scenario that could be useful are cloked Ghosts w/ Snipe or Ravens with the Hunter/Seeker Missle (does nice AOE on the air units, which tend to group up a bit)
It's hard to say with certainty, since every scenario is different -how many mutas/corruptors? mid-map, or near your base? upgrades? But there are some options available to you, just be imaginative and remember to micro.
Stimmed Marines and Medivacs with Vikings
Also, Seeker Missles.
Blinking Stalkers with Sentries
Also, Psionic Storm
Hydralisks with Hydralisks
Also, Fungal Growth
Thors + Marines with Stim.
A critical number of thors, 3 or 4, will take down a ball of mutas. The Thor anti-air has a bonus against light units, and will do splash damage. Mutas have a nasty habit of clumping together.
A few stimmed marines will greatly assist your thors. The thors will soak the damage and deal splash, while the marines chew them out of the sky.
If he attacks with more than a dozen mutas, then its even more in your favour! The splash damage will be even more effective.
6 Thors (2400 min/1200 gas) can easily take down 24 Mutas (2400/2400).
For Zerg, there's nothing better than having an army of Hydralisks - even better if you can micromanage well.