Lighting the locks. Hit the bookcase to spell G-R-E-E-D, one letter a hit. On your first multiball the game helps: the first switch you hit on each ball spots a letter, and a tilt also gives you a "cheat" letter. When GREED is spelled the bookcase swings open and shows the vault. If a ball happens to fall into the vault while the bookcase is still closed, GREED is spelled on the spot, the bookcase opens, and that ball is locked. The rulesheet calls this "dirty pool".
Locking three balls. Green lamps show you where a lock is lit. For your first multiball, ball one locks at the vault or at Thing's eject. Once one is held, the machine serves you another ball at the plunger (or fires one out of the Swamp Kickout if there are none left below). Ball two locks at Thing's eject, the vault, or the swamp. With two held, the red lamps light over the Electric Chair and the vault, and The Power magnets switch on. Shoot either red shot to lock ball three; everything is released and multiball begins. The balls come out of the Swamp Kickout, and one comes out of the Electric Chair if that is where you locked the last one.
Jackpots. Two shots are lit from the start: the Train Wreck target in the back left corner is the jackpot, worth 10 million to begin with, and the left ramp is the Super Jackpot, double the jackpot on your first multiball and triple it on every one after. After you earn either one, the vault opens; shoot a ball into it to relight the Super Jackpot. You can keep taking Super Jackpots as long as two balls stay in play.
Raising the jackpot before you take it. Every bookcase hit and every centre ramp during multiball adds a million to the jackpot, up to 25 million. The value carries over from one multiball to the next if you never earn it. Once you earn the jackpot it goes back to 10 million. The rulesheet does not say whether taking a Super Jackpot resets it too.
The restart. If you get down to one ball without earning a jackpot, you have 20 seconds to shoot Thing's eject for a restart. While that clock runs, rooms and Stars are off, Thing Flips is off, every centre ramp shot comes down the right inlane, and The Power is off. Make it and a second ball goes to the plunger; two-ball play begins the moment you plunge it, with both the jackpot and the Super Jackpot lit again. That plunge is another go at the skill shot, and from the eject the Train Wreck and the left ramp are easy shots. One restart per multiball. Miss it and, in Thing's words, "sorry old man".
The second multiball and after. GREED now takes five real bookcase hits. Only the vault locks balls one and two. Ball three can go in the chair or the vault for your second multiball; from the third multiball on, only the vault. There is no way to add a ball once it is running. It ends when you are back to one ball and the restart clock runs out.