Some ides:
Enemies.
It’s not a Mario game without some koopas, goombas, and pirahna plants. (Unless you count Super Mario Bros 2…)
Pits. Simple, you lose a life when you fall in.
A world map. You choose a level and play it. You have to beat 1 level to advance to the next.(Buttons, barriers, and teleporters.)
A mushroom, when you collect it you use a damage booster to turn red, when you hit an enemy/spike your damage goes back to 1 to remove the red effect.
A fire flower, when you have a mushroom you earn an… evil eye? that can fire enemies.
Are the cash coins? If not, some coins would be cool.
You could get coins outside of blocks using barriers that depict coins and zones that give cash and deactivate the barriers.
A door, using a button and a teleporter.
Lives. I’ve actually got a guide about that, though I doubt you’ll need it.
If cash is coins, 100 cash collected gives a 1-up.
What I’ve seen looks very impressive, I’m scratching my head over that super smooth semisolid jump.
The pipe seems like it goes in just the right amount, and the question block looks cool.
Thanks for reading my essay.