Game Maker’s Toolkit is a Youtube channel focused on game design. Videos often focus on individual mechanics and analyse different games and how they implement those mechanics. There are also videos about Mark’s own games, Word Play and Mind Over Magnet and how he designed them.
Some sub-series like Boss Keys analyse Metroidvania style games and how their worlds and the locks and keys are designed.
GMTK also runs popular game jams where thousands of people participate over a short period of time to build games based on a shared theme.