How do i change Mario's health?

[jesusyoshi54]

If you change his HP, ypu have to change all damage in the game to match it (i.e. take 1 HP), unless youre trying to make him die instantly to everything. You would also need to either make a breath meter or remove underwater damage.
I would suggest using decomp to do this. You can make all these changes by just searching for marios HP variable/enemy damage variable and changing the numbers there. You also have to change the texture to just be 3 slices.
If you just change numbers you should be able to still open the game in rom manager after compiling if thats the tool youre using.