Toonstruck

Real-time:
There are several instances of simple, minor time constraints, such as picking
up an object while a character's back is turned. These are all simple and fair
use (no death or major setbacks, if you miss the opportunity it re-appears
momentarily). There are a few that are harder:
*) getting the prizes from the Wacme machine
*) fish flushing
Even the hard ones are not too bad, and they are not game-stoppers -- just try
again until you get what you need.

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Reasonability:
*) using the music box as a royal stamp -- the box would seem to be too big,
   and it's not clear that the happy face on it has sunken eyes et cetera
The wacky nature of the setting strains reason, but most things follow well
known cartoon conventions -- the puzzles and their solutions are not
arbitrary.

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Difficulty:
The harder ones:
*) sabotaging the workout apparatus -- a good aha! problem, this could also be
   very easy if you realise the goal
*) getting the knight to raise the portcullis -- hard because you have to
   realise the geography of the place to associate the panel with the knight
*) the royal stamp -- because of silliness
There are many moderately difficult puzzles, and one or more of them could
easily be a stumper for a particular person.