The game was known for having numerous dead-ends (i.e. getting into a state where the game could no longer be completed). When you get into such a state the game doesn't tell you – you can aimlessly continue playing.
Could someone supply a comprehensive list of all the dead-end scenarios?
Best Answer
Note: this answer contains mild spoilers, but doesn't explicitly solve any puzzles.
In Maniac Mansion, the dead ends are essentially anything that prevents your characters from completing their scenario(s), and getting past Purple Tentacle into the lab.
Here are the general dead ends, which will fail the game regardless of your choice of characters:
Getting one kid stuck in the dungeon without the key, with none of the other kids being able get into the mansion
Killing a kid with an important item or ability (or perhaps an important status, such as having a character on your side), or only having one kid left when you need two to solve a puzzle. Obviously, killing any kid should raise serous concerns about your ability to finish the game
Killing the man-eating plant while you still need it
Using the paint remover in the wrong place
Being wasteful/careless with your dimes
There are also some actions that will prevent you completing one or more character's scenarios:
Exhausting the patience of the Meteor Police
Failing to develop the film correctly
Making the envelope unusable
Not collecting the package
Not collecting the stamps
Putting the wrong item in the envelope
Once you have gotten into the lab, there are no "dead ends" - the game will finish one way or another - but you may not have picked up some items you need to finish with a good ending. These items can be collected at any time before entering the lab though.