Mostly about GameMaker Studio's 2 built in physics...and how it might just be more trouble than it's worth than to just manually code everything yourself for a platformer lol. that and some other limitations to do with hitboxes, collision masks, etc. Also that building for html5 can lead to very different results from a simple exe for some reason - apparently something to do with floating point values? Either way, much of my time was spent fine tuning how movement worked which didn't leave much time for any other aspect. I guess at least it's helped me not to be fearful of messing around with things as much.