Really, it's entirely up to you. What do you
want to implement into your hack? Do you want to create something that feels like a modern Mario game, with wall kicks
and ground pounds
? Or do you still want the retro feel? Or, maybe, you want to play as Yoshi
There's no real right or wrong answer here, so whatever you do you'll get off on the right foot as say.
However, it may be worth looking through the bug fix patches
we have hosted here, too. You could consider those to be essential, I guess.