So far I’ve got:
Green pipes
Yellow ? blocks
Goombas, Koopas
Red mushrooms
Stars, coins
Boo
Piranha plants
And obviously Mario himself, and Luigi/Yoshi/Princess Peach/Bowser
Additional images: red coins, Shy Guys (I have a fondness for them), hammers, the various suits from Super Mario Brothers 3 (especially the Tanuki Suit), and I would add a Luma from Super Mario Galaxy because it would be neat to showcase icons from Mario games across the decades.
dont forget the ghosts! and the little flame dudes and those creepy plants that eat you and feathers oh and the caterpillar things from the forest of illusions