Q: "What do I do against siege/tanks and hellions as protoss?"

Edited for clarity/brevity...

Mr. Chupon: What do i do against [siege tanks and hellions]? This was on Lost Temple and I was playing protoss (low diamond level game). He was stuck in his base and i thought it was ok to expand. He was at the 6 position, me at the 3. He had expanded to his natural and I had expanded to the high yield between us, which might have been a mistake. I saw that he was going siege tanks and hellions and I thought, "no problem, stalkers, sentries, and immortals will destroy them." Well i got [destroyed when I attacked him].

It's always impossible to claim gospel truth for any situation, but I think making good, thought out suggestions never hurts.

Unit Matchups

Sieged tanks are good against just about anything in groups, dealing the highest per hit damage in the game with great range. They can't hit things that get up close and generally do poorly against fast moving units. Immortals fight siege tanks really well because of their massive damage bonus against them and their hardened shields (max of 10 damage per hit as long as shields are up- guarantee of at least 10 hits before their shields fall).

Unsieged tanks do decent damage in general, but aren't terribly cost efficient if they're taking damage. They're especially good against armored units.

Hellions do good AoE damage, especially against light units. They're also one of the fastest units in the game. Against non-light units, and ranged units in general, they tend to fare poorly.

Zealots would beat the siege tanks normally, but the hellions are there to counter that. Stalkers get beat up by siege tanks pretty quickly, but blinking stalkers could take minimal damage on the way in and focus fire the siege tanks down quickly. The damage of the hellions shouldn't be significant against the stalkers.

My actual suggestion here would be to tech straight to void rays, actually. He's not pushing out of his base at any fast rate against stalkers/sentries/immortals. The siege tanks are the only ones that can lay out any hurt against that, and they have to slowly siege and resiege to do that. I'd cede ground very slowly while getting void rays. The gold minerals will give you way more $ than you know what to do with. I'd nexus someplace else immediately and put up the 2 assimilators while you're at it, since you're going to need the gas to support double startport + normal unit production. I'd keep immortals building nonstop, and with the extra minerals invest in some zealots or photon cannons (just to slow him down if he attacks you when you're unprepared). If you still have extra gas with chronoed immortals and void rays, I'd get either another robo facility for more immortals or get blink for your stalkers, depending on how many of them you have.

Strategic Level

You made a big mistake by attacking him. Siege tanks fail at taking ground because of their setup time and vulnerability to flanks. If you have an advantage (which you did here- a better army on open ground, and the gold expansion) sit back and use it. Don't press your attack unless you absolutely have to or know you have a great opportunity. Make him come to you. Attacking siege tanks is bad- your observers should have told you this. Keep expanding while you keep him sealed.

Day9 put this well in one of his videos: Any time you're feeling confident that you can bust into his base and win the game, take a deep breath, relax, and expand. That will win you far more games in the long run than most any other tactic. Don't risk stupid losses by rushing victories. There's nothing more frustrating than being on your back foot and watching your enemy expand and make an even bigger army and economy instead of going in for the kill.

While we're on the subject of expansions, don't expand to the gold of a terran going mech. Siege tanks are just too tasty to pass up. If he had a MMM build, that would make a lot more sense, because it'd be easier to defend than the gold on the other side of the map.

Micro Level

At the micro level, use an observer to scout his ridge. Chances are his siege tanks are siege on the ridge, but the hellions are down below to prevent attacks. Bait some zealots to eat the siege tank shots then blink your stalkers to them point blank and kill his tanks. Blink back down when his reinforcements come. Hopefully you'll have only taken shield damage at most. ONLY do this if you have to pick off some tanks for some reason, like him pushing before void rays are ready. Like I said, don't attack unless you need to.

Immortals can easily bust through his army, but just because immortals take dramatically reduced damage against tanks doesn't negate the sieged tank's range advantage and high ground. In an open field fight have your immortals target the tanks, but don't try to bust through his front with them (or any unit, other than air).

Follow up

Q: : Do hellions actually not do a lot of damage against satlkers?

A: Hellions do a whopping 3.2 damage per second against a single non-light unit, not including armor. Best case scenario, it would take an upupgraded hellion 50 seconds to kill your unupgraded stalker. Yes, they do awful damage.

Q: Aren't hellions good against immortals because they do less than 10 [and thus don't suffer reduced damage from the hardened shields ability]?

A: See above. At 3.2 dps, it would take a single hellion 31.25 seconds to take down just the SHIELDS of your immortal. Immortals kill hellions in two hits. Just because immortals don't get the shield ability bonus against hellions doesn't mean hellions are good against immortals. The best counter to immortals are rapid firing units that do around 10 damage. Hydralisks go great jobs, as do stimmed marines. Zealots (count as 2 separate attacks, so it does the full 16 and not just 10) and zerglings are the same way.