Note I've only played the TGPA demo as of yet. It's a nice hack, I had some trouble in a few areas because of my skills. I found a few issues:
World 1-4 - Piranha Forest
The fish aren't swimming because sprite buoyancy is disabled.
World 1-Fort - Sledge Bro Fort:
Defeating the Sledge Bros. results in the vanilla water theme playing.
World 1-5 - Lake Side Passage
This red coin is black.
World 1-Castle - Serious Passage
I think this part here with the Hammer Bros. is a bit hard to get past without taking damage, but it may just be me. They also take much longer to jump.
And I was expecting a boss but ok.
World 2-2 - Cyan Walkway
Some events have wrong tiles. The events are from World 1-3 - Ruins in the River (secret), World 1-6 - The Abandoned Cave and World 2-1 - Bubble Path.
When you enter a level, it says MARIO START!
I played the hack without using save states or rewinds. I died a few times in 1-Fort and 1-Castle, then a lot in 2-1 until I had 3 lives left because my skills aren't the best, and I also noticed there's no 1-2. The first level is 1-1, and the second is 1-3, skipping 1-2. And sometimes nothing happens when throwing something into a Bro. enemy.