GAMEPLAY UPDATE:
I've just included a few items that can help you out on your quest.
TRAM REPAIR: Adds 25% more health to your health bar.
CANNON COOLANT: Lowers Proton Cannon's temperature gauge by 50%.
TIME-STOP: Freezes the timer for 5-10 seconds (each one is variable, but still stays within that area).
TREASURE CHEST: Contains any one of the three items.
WHEN FIGHTING BOSSES: Any time you deal extraordinary damage to a boss, any of the above items will fly from his grip and into your possession. You have to be especially creative when attempting this, but usually you can gain an item by slamming the Boss into a wall, ceiling, or floor.
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HARD MODE CHALLENGE:
Beat the game with at least 75% tram health left and within, oh, say 5 minutes or so.
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METHODS ON BEATING BOSS GHOSTS:
SLIMER: Blow up food items he's going for when he wants to recharge his health. Also, tangle him up in the chandelier, then knock it down.
KILLER JACK: The three “strength tester” games are quite useful here. When Killer Jack moves in to attack, lift the weight with the Proton Beam, and FLING it up to the bell. The impact of the weight on the bell will KO the evil clown, stunning him for 3 seconds. This is your chance to attack him. Be careful, though–his hammer packs quite a punch.
THE HOBO: Just keep him in the beam for as long as you can each time he attacks. Oh, and keep a sharp eye on the upper and lower corners of the screen.
THE THREE-HEADED MONSTER: You'll have to go in for the old one-two-three. First, attack the small head on the left, then the small one on the right, then the big one in the middle. Also, he'll throw Fire Ghosts at you. They act a bit like very pervasive homing missiles, but you can use the Proton Beam to throw them off course and back to the big guy. This will do about 15 points damage to him and give you an Item.
GOZER: Gozer's acrobatics pattern is as follows: A-B-C-A, A-C-A-B, A-C-B-A, and then she rinses and repeats, throwing lightning on each jump and when she gets back to the starting point. Here, A represents the middle of the arena (the Temple Doors), B represents the far right of the arena, and C represents the far left of the arena.
Anticipate where she's going to land and fire the Proton Beam at that area *before* she lands. The timing of this is pretty tricky, but it's worth it: the initial attack will deal 20 points damage and stun her for 3 seconds, allowing you to capture her in the beam. Remember to shoot the lightning she throws. Each bolt does 5% damage. This adds up very quickly.
MR. STAY-PUFT: Shoot him in the mouth each time he appears. It'll do about 50-75 points damage each time, because he'll duck back behind the temple real quick-like.