Ok a rundown here....
Bullet Bill- Your kart turns into bullet bill, and you jet in front of a buch of people
Orange & Red Mushroom-Your kart gets big, and you can run over opponents
Red Shell-Shell locks on to a target
Green Shell- Goes in a straight line, can be dropped
Banana-drop or shoot it forward, opponent will spin out when it runs over a banana
Blue spiky shell-Takes out the person in first place at the time
Blooper (Squid)- Covers an opponent's screen (I think 1st palce) in black ink bloking their view
Fake box-Will cause an opponent to spin out if they try to pick it up.
There is a lightning one, but I don't know what it does, I think it shrinks everybody elses karts.

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{Spur of the moment Toad Mario Kart poem below! lol it is bad!}