The mouse traps on Mousin' Around might be among my favorite locks in pinball, and they fit the theme perfectly. The coolest lock though, imho, has to be the prototype lock on Judge Dredd. That thing is really cool to see in action, and I can't think of a more unique ball lock. Oh, and I love the Time Expander on Doctor Who as well! That game was created with an original story centered around the Time Expander, so theme integration is superb in that game.
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