I think when people mean that Discworld books have become darker they really mean the series is growing up. In 'The Colour of Magic' most of the city is set alight. It's a joke, in much the same way that the Earth is destroyed almost at the start of Douglas Adams's 'The Hitchhikers Guide to the Galaxy.'

One thing that writers have in common is that they are readers first. They have read lots and lots of stuff, because they're just infested with lots of stuff.

We who think we are about to die will laugh at anything.

Never trust a species that grins all the time. It’s up to something.

Whole new theories of money were growing here like mushrooms: in the dark and based on bullshit.

As large as worlds. As old as Time. As patient as a brick.

The thing about witchcraft," said Mistress Weatherwax, "is that it's not like school at all. First you get the test, and then afterward you spend years findin' out how you passed it. It's a bit like life in that respect