Mario Kart Wii Items

Trap Items

Banana

These items can be placed on the track whenever you press the item button. Getting a normal one gives you one banana, getting triple bananas gives you three that follow the kart until you've dropped all of them. Since they cause karts to spin out after going over them, it is recommended that you place them in areas where other players either can't see them, landing spots from jumps or on booster ramps so players fall off them.

Fake Item Box

This is a fake item box, and generally looks like the real ones you get items from. However, it is slightly tinted red, and just looks different in general to the real ones, with an upside down ? mark. This makes karts somersault on hitting it, so it's best to place either where you'd put a banana or three or right on top of a real item box.

Bob-omb

An explosive enemy which is an item since Mario Kart Double Dash, you can either throw these ahead at opponents by holding forward or simply drop them behind your kart. They cause karts to fly into the air. On another note, you can also hold them behind the kart or bike, but this is incredibly dangerous if another player rams into it...

Speed Boost Items

Mushroom/Triple Mushrooms

One or more items which give a short speed boost, useful for cutting across off road, taking shortcuts and dodging certain items. You also get three of these in time trial, and they can also fall on the road, giving a speed boost to any player which goes over the dropped item.

Golden Mushroom

Originally Toad's special item in Double Dash, these have also been in recent games and give any player the ability to constantly boost until the mushroom vanishes, going incredibly fast and having any of the uses of a normal mushroom.

Shells

Green Shell/Triple Green Shell

A basic shell which, when fired, goes straight and then bounces off a few walls. These items require aim to use against opponents, and can also be used as a shield by holding them behind you. Three green or red shells makes a three shell shield appear round the character which can allow you to nicely ram opponents to spin them out...

Red Shell/Triple Red Shell

This is a shell or three shells which, when fired, home in on the opponent in front. They can also be used to block attacks.

Note: Red Shells don't hit opponents who are too far away from the track, or who are using a cannon, or sometimes who are just using a ramp and in the air.

Spiny Shell

A blue shell with wings which homes in on the first place player and blows them up. Like a homing shell come bob-omb with wings. However, it will also affect any other characters in the blast radius by destroying items and hitting them, will go for the first person who is STILL racing, will not hit players in cannons or launchers, can be dodged with a well timed mushroom and will hit the user if they're in first.

Note: Supposedly hits the first person on the other team in team mode vs play.

Invincibility Items

Star

Makes your kart invincible, allow you to send karts flying by ramming them, have increased speed and cut across off road with no slow down. Oh, and while invincible, you are immune to all enemies and items including blue shells and lightning bolts.

Bullet Bill

Makes you into a Bullet Bill, which takes your kart through the next piece of track on auto pilot at high speed, knocking aside any kart, item or enemy character that happens to be in the way. While a Bullet Bill, you can barely steer away from the main, default track, and any items in the way are destroyed.

Note: Unlike the Chain Chomp from Double Dash, this item will never send you flying off the course while in effect, and can go through cannons and launcher devices.

Mega Mushroom

An item that makes you huge, a bit faster and able to crush any vehicle you hit. You are also immune to all items in this form. The downside however is that compared to the Star and Bullet Bill, this item is rather short lived...

Other Items

Lightning/Thunder Bolt

Makes all opponents spin out, shrink and lose their items. You can then race past at normal speed while the shrunken opponents go much slower.

Note: Only affects opposite team players in team mode, and opponents recover by rank, with those at the back recovering quickest.

POW Block

Right from Mario Bros, this item causes any opponents in front of you and on the ground to spin out. This does not affect airborne vehicles.

Note: You can dodge this by doing a trick or wheelie on the last part of the POW block to avoid spinning out. However, you still lose items.

Thunder Cloud

Gives you a cloud above your head which makes you go faster for a while. However, it then, after a short time causes lightning to come down and shrink the player using the item, so it must be passed on by touching another player.

Blooper

A pretty pointless item which causes ink to appear on the screens of your opponents. This may backfire if you are in first place, just like in Mario Kart DS.

How to get each item

You get items by rank in the race at the time you pass through the item box. So if you are nearly last, lightning and bullet bills are far more common while at the front, only weak items like banana skins and green shells are available.