This is an article explaining our somewhat mathematical approach to designing difficulty curves (or difficulty progressions) into games! It was originally an internal document which we used when making games from around 2005 through to 2010, where arcade and action-puzzle games formed the majority of our output.
TL;DR : This is an article intended primarily for other developers who are developing games which get more difficulty with time or level. The solution at it’s simplest is to work out how well the best possible player could play, and adjust based on that! Note – this gets a bit more technical than everyone may be happy to read!
TL;DR/2 : There’s a mild dinosaur reference in this article!