This is a general item tier list for Mario Kart World based on their offense, defense, speed, and impact. With a small descriptions for each individual item.

Coin: Besides giving coins to the user, this item becomes more common the more ahead your placing is. Its best use is when a Boo steals this from you.

Banana: This item stays in place where it lands after thrown ahead, or if dropped.
Blooper: 1 blooper comes out, a bunch of people get their face and eyes covered in black ink.
? Block: Gives some coins, and can actually give some small bit of a speed boost.
Green Shell: Requires fair skill to successfully snipe another driver.
Red Shell: Eh
Hammer: Briefly linger where they land. A lot of hammers come out.
Triple Banana: Some defense.
Triple Green Shells: Cover an area with bouncing shells.
Fire & Ice Flower: Can be used to throw back at people throwing shells at you.
Triple Red Shells: Better thrown offensively ahead. Sometimes orbit defense is better.
Boomerang Flower: Breaks shells and bananas.

Feather: Requires some bit of skill.
Dash Food: These don't work 100% like mushrooms.
Bob-omb: Can scare drivers behind trying to get speed boost.
Kamek: Can summon a lot of random shit to hit others.
Coin Shell: Travels down on the middle of the road hitting others. Good for coins.
Super Horn: Fair offense. Good defense.
Dash Mushroom: Very good for shortcuts.
Spiny Shell: Fast, big. Homes to lead blowing up on them. Can hit other drivers in its way.
Triple Dash Mushrooms: Can also be used to reach top speeds.

Super Star: Uncommon item. Can be used with Dash Mushrooms.
Boo: Can be used to evade obstacles on the road.
Mega Mushroom: 2nd best mushroom next to gold.
Bullet Bill: Just broken over powered.
Golden Dash Mushroom: No invincibility. It's like 9 Dash Mushroom

Lightning: There is no item more bullshit than this. There is no item that can make some one have the most unfair bullshit lose. Very uncommon item.