As of 3/11/12, the Golden Age Player's Guide says :

"Multiattack
Once per turn, give this character a power action. It can be given
any two actions as free actions. Resolve the first free action before
giving it the second.

Double Power Actions
 In order to use a double power action as a non-free action, a
figure must be able to be given two action tokens.
 When a double power action is given as a free action, no tokens
are placed on the figure"

It seems that Master Mold can use Multiattack as a power action, which grants him 2 free actions. He may then be given a double power action for each free action in order to use Sentinel Assembly-Line twice. No action tokens are placed on the figure when a double power action is given as a free action. So he ends up with one action token resulting from the power action given to activate Multiattack.

He could then do this on the following turn and could use colossal stamina to keep doing it each turn thereafter, because as long as the double power actions are given as free actions it does not require the figure to be able to be given two action tokens.

Very close to accurate but the last line is wrong. Because he HAS a token from the previous turn there is no way that he could then use the Multi-attack to give two more free "Double Power Actions" because since he has one token, he would not be able to use that power. Now what he can do is this.
Turn One, Multi-Attack Double-Power Action, Double-Power Action turn the factory dial 4 times so far
Turn Two, Multi-Attack Power Action(1 Turn), Power Action (1 Turn) Factory turned 6 times so far, colossal Damage next turn to keep doing this.. OR

Turn Two Clear MM,
Turn Three, Multi Attack Double-Power Action, Double-Power Action, turn dial 4 more times for a total of 8 turns and no Colossal Stamina Damage

Just REREAD the ability and yes Milo you are correct my mistake I head to read the DPA power three times for it to sink in as they say before it hit me since he's using the DPA as a FREE ACTION granted from Mutli-attack it never checks to see if there are action tokens it doesn't care.. Very nasty indeed.

Apparently he can. As someone pointed out to me, from the Players Guide: "In order to use a double power action as a non-free action, a figure must be able to be given two action tokens." Through Multiattack he's using the DPA as a free action, so the number of tokens on him do not matter. He can Mutliattack DPA all day long.

So what was the consensus on how many sentinels can be on the board at once? Does it have to be under 300 per the sentinel point value or under 300 per the remaining starting force that Master Mold began the game with?

And does the opponent get points for each sentinel KOd?

Lastly, Should the sentinels be popped out so it gets as close to 300pts as possible and then pop out the super-booster 300pt sentinel to bring it over 300 pts?

It's 300 points not counting him, doesn't matter if the remaining 300 is sentinels or all Lian Harper Pogs (good lord 300 of her shudder) So for example you have a 900 point Build, you bring the Master Mold at 700 and 200 other figures (for this example we will use a 200 point Advanced Sentinel) you can use the MFG plant to pop out any sentinel up to 300 points, once you pass the 300 points of additional pieces you can no longer use it to make sentinels until the others have been KO'ed.

Your best return in this example would be to pop out a Omega Prime Sentinel for 59 points, let the dial spin up to 300, then pop out 300 point sentinel (you could also use some of the Sentinel Troopers from way back as long as you don't go over the 300 mark you can always bring in something)

Your opponent would get any figures that are KO in the match, doesn't matter how they were brought in.

Now if we were playing in a 700 match and you brought MM I would suggest this output of Sentinels.

Turn 1, MA to Turn dial 4 times, bring out two Prime Sentinels, Total points added so far 118
Turn 2 MA to turn dial 4 times, Bring out a 150 point Sentinel, Total points added so far 268
Turn 3 either Clear wait for next turn, or Push using Colossal Stamina, since your total is still under 300 minus Master Mold, activate MA to turn dial 2 times, bring out a 300 point Sentinel, and then attack or move MM somewhere. So now you have an extra 568 points on the board to smack your opponents with, but keep in mind now you will have to WAIT until the 300 point sentinel is taken out before you can bring in any more. Also your opponent does get the victory points if he/she knocks those characters out. Hopefully this explained everything.

Correct my earlier comments you are correct!

Is there even a strategy against this guy at 600pts? It seems like he's the best 600pts. Especially now that CW005Sentinel and GSX003Omega Prime come out first turn to tie up your opponents until you can get your GSX Sentinel Mark II/V out. It seems rather difficult to beat him. Anyone build a team that can take this guy out at 600 pts?

Also...when/IF you KO him...is it game over or does the team he spawned continue the battle?

He is beatable, but it is very difficult. It helps to win map choice so you can put him in the prison or another tight map. The tight maps along with your characters can keep him from having the space to place the colossal sentinels. I got extremely lucky and pulled out a win with the skrull chases, skrullbolt, yellowjacket, and some old LE skrulls.