Hauer

One of the Hulks lesser known abilities is to detect astral forms.  You used to see it in the early Defenders book when he would be contacted by Dr. Strange.  
   I think it was just was just Detect: Astral Form/Ghosts.

The simplest thing would just be to take Detect Ghosts for five points and assign it to the Sight group. There, you can see ghosts now.
 
If you're building something like the Ghostbuster's PKE meter, you start with an appropriate Detect power and build it into a focus, with whatever adders and limitations seem appropriate.

I'm not sure what you're looking for. 
Do you want to be able to see invisible entities as though they weren't invisible?  https://www.herogames.com/forums/topic/97998-see-invisible/?tab=comments#comment-2700554
Do you want to just know when something invisible is near?  Build a Detect Invisible sense or Detect Ghost sense with whatever modifiers such as range make sense.
Do you want to be able to fight invisible entities?  Make one of your other senses Targeting (maybe the aforementioned Detect). 

That's where the OIF (-1/2) bonus comes in.  As we saw in Captain America: Civil War Tony didn't have his Armor when the Winter Soldier broke out of containment.  A -1/2 limitations means you don't get  to use your powers half the time.  A -1 for an OAF means that at some point someone will make a grab for the thing in a fight.  Wonder Woman knows that from the number of times she's been bound by her magic lasso.

See the "Adjustment Powers" section on 6E1 135-143. Typically points removed by a Drain (or added by an Aid) are regained  (or lost) at the rate of 5 Character Points per Turn, but there are Advantages and other factors that may affect this.

Your GM is incorrect (unless, of course, he wants to change how the Advantage works -- it's his campaign, of course). As described by the rules on 6E1 342, Penetrating means that a certain amount of the damage gets through, based on the amounts shown on the dice. I haven't double-checked the math in the example you gave, but the methodology is accurate.

Actually the Iron Man cartoon from the 90's show a good example of this. Tony was a Multiform who would transition armors in the field.  James was an OIF (maybe OIHID)

Here's a point that sometimes causes arguments, but is BtB: the base form (the one that pays the points for the Multiform power) is not necessarily the one built on the most points.

That means that the Hulk doesn't pay points to turn into puny Banner; puny Banner pays points to turn into the Hulk.
 
The idea is that you don't pay points to become less powerful.
 
Of course, arguably you are getting the abilities possessed by the Banner form for free. The offset is that the Banner form is less powerful, and transforming into the Hulk can theoretically be prevented.
 
As always, the GM should look very hard at characters who use this kind of construct, and as steriaca suggested, say no if they are unsure.

A good idea! But remember that the trade off is armor thickness—weight — horsepower. The Japanese Type 95 Ha-Go, is a sprightly little scout tank, but it’s high top speed is because that engine is not over burdened be its thin armor. The King Tiger at the opposite end, has a 12 cylinder Maybach engine, but it’s superb armor limits it’s speed and hill climb ability. But it can push over a building, whereas theType 95 can’t. I think the base attribute would be the base weight of the vehicle, with the horsepower calculated to get ground speed in the right ball park. Armor thickness is back calculated from what it can always bounce. Can it shrug off .50 caps but not 20mm? That can give you a pretty good indicator of its defenses. 

As discussed on CC 156, an attack's Damage Classes (DCs) are determined by its Active Points -- 1 DC per 5 points. So let's suppose you have an HKA 2d6. That's 30 Active Points, which means the attack has 6 DCs.
 
The methods for adding damage are discussed on CC 157. For an HKA, the most common method is Strength (STR) -- for every 5 STR used with the attack, you add 1 DC. So let's supppose your character has 20 STR to use with his HKA. That means he's adding 4 DCs, so his attack has a total of 10 DCs (6 from the HKA, +4 from STR).
 
An HKA with 10 DCs does 3d6+1 damage (unfortunately CC doesn't explain this anywhere that I can find, but I may have overlooked a chart or rule). So as discussed on CC 156, you roll 3d6 for the BODY damage and add 1 to the total. Then roll 1/2d6 to determine the STUN Multiplier.
 
Adding damage tends to be one of the trickiest parts of the HERO System rules, so don't worry if you don't grasp everything about it right away. Keeping working with and using the rules, and eventually it will become second nature. The HERO System Basic Rulebook and Volume 2 of the 6th Edition core rulebook both have more information on the subject, including some handy tables that make calculating DCs easier.

I have Champions Complete rulebook and try to understand. Probaly its easy, but i cant find answer. 
On page 156 is about damage. I completly dont understand how calculate DC (damage class) to damage dices? 
For example: how i know how many dices add to HKA if I add 4 DC to attack? 

I have Champions Complete rulebook and try to understand. Probaly its easy, but i cant find answer. 
On page 156 is about damage. I completly dont understand how calculate DC (damage class) to damage dices? 
For example: how i know how many dices add to HKA if I add 4 DC to attack? 

Depends on the source Tony. Base armor under my skin Tony can get away with not buying a focus and going with multiform on Only In Alternative Idenity except for a few basic powers in all forms. 1980's Tony still had to carry that briefcase around with him wherever he goes.

Remember, the GM has to okay the character first.  Just because the rules say you can do something doesn't mean that a GM will allow it in their game.  
 
The point of Multiform isn't to be able to get "free points" (he says, glaring at his 1986 self).  It's to have a way to be able to switch into multiple forms and to have a way to appropriately charge points to do that.  There are a number of warnings to and safeguards from the GM that go into using Multiform.  

Say you have a Tony Stark character  who has several different types of Powered Armor.  Mutliform: 4x 250 Points would give you four different sets of armor for any situation you could think of.
 
I used the 5th Edition Rules for it's cost.

Multiform is not for beginning game masters. I advise beginning game masters to Nancy a character with one.
 
There are reasons for Multiform. It is the best to repersent someone who not only changes powers, but personalities also.

Thanks for answers  Chris, where I can find examples of warnings and safeguards for Multiform :>?