Sign, I guess I broke my promise never develop a mario game again. 
It's just something so fun to do during my spare time besides hanging out with my bros.
Anyways I present the only accurate SMB2 engine up to date:
Supernova Mario Bros. 2 Engine (Saturn Mario Engine 4)
Platform: Game Maker 8.0 (Pro)
Which features (including planned):
Downloads (It will update every time when a progress is posted):
Current version Zipped [4.32 MB]
It's just something so fun to do during my spare time besides hanging out with my bros.Anyways I present the only accurate SMB2 engine up to date:
Supernova Mario Bros. 2 Engine (Saturn Mario Engine 4)
Platform: Game Maker 8.0 (Pro)
Which features (including planned):
- Generic SMB2 pull-n-throw system
- Some additions from Super Mario Advance (GBA)
- Jump-through slopes (? - that I'm not sure)
- Character selection system
- Organized coding (Easy to switch key options and global functions uses an object called obj_SYSTEM instead of global.[function] which reduce system memory usage) [Thanks to DarkBlueYoshi and Kremling]
- Subspace system
- No Game Maker's built image transformation, it messes up the collision boxes
- FMOD music system
- More to be planned.
Downloads (It will update every time when a progress is posted):
Current version Zipped [4.32 MB]