Starcraft – How to counter widow mine

For protoss you have to make excellent use of Sentries to delay your enemy. If possible, try to split his army in two with Force Field(s) and take on that half by itself with your zealots, sentries, and stalkers. You won't be able to take him in a head-on fight as Marines/Marauders dominate your T1 units.

Use this delaying tactic to get a few Immortals as soon as possible and transition into Colossus with the range upgrade. The splash damage is very effective against the tightly clumped Bio Ball, while Immortals can take many hits from Siege Tanks. Use Blink Stalkers to get close to the tanks and focus them down. Note that once you have a few Colossi, your opponent will usually get a few vikings to counter them, but focus them down quickly with your stalkers.

Honestly, it is a very difficult thing to beat as Protoss if your opponent is of better or equal skill, especially since you have to tech to very expensive units just to counter his (mostly) T1 army. You'll just have to delay and outplay them and not make any mistakes, and make sure you are very proficient with your Force Field and Guardian Shield usage.

Another option is to go High Templars with Psionic Storm and Feedback on the Medivacs, but I rarely go this route as it is too gas-intensive and higher level Terran players will just use Ghosts which nullify High Templars with their EMP ability (Removes all energy and 100 shield points). Not to mention if your clump of High Templars goes within range of a Siege Tank you're dead meat.

Dealing with a cannon rush as Protoss is very different from dealing with it as Zerg. Creep prevents the placement of buildings in a lot of places, so a cannon rush against Zerg is largely used as a contain. This is not true for Protoss.

A number of people have suggested countering, or getting up defense, or expanding, but against a standard cannon rush (8-10 Forge) chances are you don't have time for any of that. They should be finishing their first cannon around the same time you are finishing chrono boosting out your first Zealot. With a very early cannon rush like this, if you do not catch them throwing down that pylon, you will not survive. They've made a huge economic sacrifice and this will be an "all-in" for them.

This is a very scary situation to be in and even at high levels (~1200 Diamond) a fast cannon rush like this a guaranteed win if its not scouted (and still 20-30% effective when it is). I'd recommend the following recourse:

1. Don't panic. Disaster management is a very important skill and if you panic you won't handle this well
2. Don't pull all your workers. This is a classic mistake, as they'll just let them target his Pylon, throw down a new one and cancel the old
3. Kill the Probe. This is usually hard (as you only have probes) and you'll have to pull workers off and micro a surround. Since Probes can build far more than you can destroy this is your number 1 target. This will be especially hard since they can avoid any surround by just clicking on minerals (workers get unit walking while harvesting). Keep attacking them and pull in more Probes as needed.
4. Throw down a Gateway. You should catch them before you'd normally do this so this should be one of your first instincts. Probes can't do enough damage to buildings, you'll need this to clear them out.
5. Don't cut Probe production. While you'll shift your chrono boosts to Zealots (save them while waiting for you gateway), you still need to build your economy. The goal of fighting off this rush is to survive and come out ahead. If you cut Probe production you will not come out ahead.

I highly recommend you practice against this with a friend. Go on Lost Temple and have them sneak a pylon in the back of your base so it overlaps the cliff. They'll follow up by putting their forge on the low ground and the cannons on the high ground (that means 2 probes). If they get out the first two cannons before your Zealot arrives, restart. You want to nip this in the bud.