I have a few suggestions:
1) Banzai Mario World
An interesting gimmicky hack with a lot of great challenges and beatiful palettes.
2) Kaizo Mario World
This hack has some enjoyable challenges, but you only have 5 lives. If you play with savestates, it won't cause many of problems. If you don't mind its aesthetics (like maybe floating/stacked munchers), you should play it.
3) Korosu Mario World
Although it has 'Mario' in the name, you play the hack as Luigi. There are a few difficulty spikes, but they aren't really significant since the challenges are overall great.
Go fix your goddamn mobile app, YouTube!