Originally posted by Ondore's Lies
Instead of making a new hack, make a new level. Work that one level until you feel satisfied with it. Then, repeat the process, one level at a time. When you feel inspiration dry up and you can't coax another new level out of your brain, congratulations. You have just successfully completed a hack, you just need to polish what you've already made.
instead of focusing on "making a proper game" remember that this is an amateur medium and there shouldn't be any qualm in making level collections of any sort of length or consistency tied together with a overworld and final level (optionally a few bosses if you can code and are feeling motivated enough to do so, koopalings+big boo+reznor+bowser are absolutely fine and much preferrable to a lot of custom bosses). that's honestly how im planning to make my hack which is why i'm expecting development to go by at a glacial pace, but i don't mind.
i was personally inspired by the vips and other collabs' development method which is just "claim levels, fill them up, start a deadline near the end, fill them up even further until you reach a deadline, then make the final multiperson and storehouse levels in the space between normal level submission end and release"
it's even better for me as an asmer because if i want to make a boss or gimmick, i can just put whatever and try to work out the gimmick to its utmost in one level and just keep it to one or two levels. don't have to worry about plot consistency or revisiting gimmicks for the most part.
i still have to be careful so it's not too much of a tech demo of course, for that i'm just thinking of following the four stage level design method from later marios. planning out a level according to a method and redoing parts as i come up with more setups and spins on a gimmick instead of playing it entirely by ear feels more "sensible" to me.
tl;dr: just make levels instead of full games