What is the best counter to mass marauder while using a standard build order? I have tried charge zealots but the just get kited to death. High Templar with storm do not do enough damage. Colossus are also easily sniped. Void Rays are good but switching to air is sometimes not an option when you have already built production structures. Maybe zealots and archons? Does anyone have a successful counter to this?
I'm not sure how each one of your examples are not working as they are viable with a little bit of tweaking.
I notice that you don't have any sentries listed there and they do help in your fights, guardian shield reduces the damage from marauders and they also provide your best ability to deal with them, forcefields.
- Immortals are also nice against mass marauder before you have colossus tech (or if you don't want to go colossus tech). But since immortals are so weak against marines, if you have the APM for it, focus them on marauders. Immortals get a +dmg bonus vs marauders and will absolutely destroy them. A zealot army mixed with immortals (assuming they go pure marauders) will make short work of the terran army. Again though, if you're getting kited, you need to know when to pull back and not take damage you don't have to.
- Charge zealots + sentries with forcefields will stop them from retreating and kiting you. Zealots do insane amounts of DPS when they can hit.
- High Templars are difficult to use because they can kite storms. But again, used with forcefields it forces the marauder to take the full 80 damage. But changing them into archons could work as well.
- Colossi are only easily sniped if you're not managing them properly. Colossi with enough of a ground army support is your best way to deal with mass marauder (My opinion). The reason being is that you would have sentries to create an area where they cannot hit your army, but you can hit them. With a range 9 with the thermal lance upgrade compared to the 6 of marauders, throw in forcefields and your colossi pick off marauders with ease and causing splash damage.
Combining all of the above will make mass marauder completely useless against you. A protoss death ball with enough sentries, zealots, stalkers, an immortal or two, and colossi can split their army in half, lets your chargelots hit the ones inside the forcefield (yes they'll get hit by the ones split off), lets your stalkers fight a smaller force, lets your immortals obliterate the marauder numbers, and lets your colossi rip through the close ones before attacking the farther one will destroy their army. It's a bit micro intensive, but probably the best way of handling them overall.
Zealots + Sentires, is THE BEST option, the only obstacle is learning how to places FFs.
Here is the guide for that Using Force Fields Effectively
How To Cast Force Field
Assuming F is the hotkey for Force Field (F is the Default) the to best ways to cast it are:
F > Click each Force Field individually, or,
hold F down and click for each Force Field you want to cast.
This is purely personal preference, I use the first option because I feel it makes me place each Force Field a little better than if I use the second option. Try both and decide which is more comfortable for you. Do not Shift+F Force Fields as it causes the Sentries to cast after they kill the current unit that they are attacking.
You're asking the wrong questions, consider these:
How do I notice that my opponent is going for mass marauders?
Scouting is key. The point of a fast-paced strategy game like StarCraft II is decision making in time, in order to win you need to make the right decisions and execute them before your opponent does. So, it is important that you gather information about your opponent; earlier is better, but not too early.
Read this post by our fellow tzenes, it contains lots of options for scouting and where to pay attention.
In order for your opponent to go mass marauders; he would be going for multiple Barracks all supplied with a Tech Lab, and you would notice that he mainly has Marauder units rather than Marines. If you want to take it to the next level, you could also pay notice at what upgrades he got from the Tech Lab. An early Concussive Shells could be a good warning sign...
What are good accessible units that easily allow me to take down the mass marauders?
Let me first tell you which units are not right, and why; some of which you listed first:
Zealots won't work given the Concussive Shells, adding Sentries is an tricky option.
High Templar and Colossus are too far along the tech path, they will come in too late.
Void Rays are too far along the tech path, they will come in too late if you planned multiple gates.
Archons, to aid your zealots; will also come in too late as you will need High/Dark Templars.
Now, if we take the tech tree and start scratching the wrong options, it gets interesting:
Stalkers, armored unit, later possibility to use their Speed and Blink to waste Stim Packs.
Immortal, armored and shielded unit, extra damage against armored units like Marauders.
But they also have their downsides:
Stalkers, they get slowed down into a crawl by concussive shells.
Immortal, very bad against larger groups of Marauders.
Can we live with the drawbacks?
Stalkers can be used in a defensive setting, this way it doesn't matter if they are slowed down. Immortals don't really have a problem because the Stalkers serve as a good meat shield for them.
So, yes, the advantages outweigh the drawbacks.
What happens after I build up my first defensive army?
You've probably guessed it, you are going to get outnumbered or your opponent changes tech. But, as I said in the beginning, scouting is key so you should have made a single observer to figure out if he is teching to something else at home.
Let's check both options:
He is going to outnumber me, what should I do?
Notice how we are in the next phase of the game, where you defended your base and you do now have a Robotics Facility available. Guess what? You can easily tech to Colossus from here. Or perhaps, you could try to get void rays instead. It's up to you, but consider the extra delay and your scouting information...
Given that you have obtained a considerable Stalker/Immortal ball, you should be able to use them to defend your Colossus. Simply by blocking the way for the Marauders; if they choose to try to break through instead of fire, they should simply die.
He is changing technology, what should I do?
Note that he is losing resources and focus because he is building and researching different technology, this is your key moment to use your ball to take down one of his expansions if you get the chance to. If he lifts his buildings, your Stalkers solve that problem.
Simultaneously (yes, an attack is the moment that you can safely do things back at home unless your opponent chooses for an unfortunate base race), you should tech to a counter for your opponent's choice. You already have Stalkers to handle air units, Immortals to handle Thors, an observer to follow Ghosts so it might be a matter of just producing more in some cases...
The ideal composition against mass marauder (potentially with viking support) is Zealot (with charge) and Archon. Stalkers are useless and Immortals are good in theory, but they are easily target fired and difficult to mass produce. Templar are also good in theory, but with stim, storm dodging is very easy and templar are easily picked off and/or feedback'd.