Items

Items come along in cubes, emblazoned with question marks, which are scattered around the tracks. You never know what you're going to get in a cube, but your chance of receiving the most powerful items is proportional to how far down the leader board you are; if you're in first place, you're never going to get a character-specific Special Item, for instance. Item cubes come in either single or double configurations; single cubes will only equip the character in the rear position with an item, if he or she doesn't already have one; double cubes will give both characters an item. You can, of course, switch drivers so that a character without an item is in the back seat while driving over an item cube, then switch back so that your character with an item is ready to go while the roulette wheel is deciding what the driver's item will be. Learning to quickly switch characters like this will be quite helpful in keeping your item supply topped out.

What you get when you pick up an item cube is random, although you have a better chance of getting a Special Item that's unique to your character if you're in the 3rd through 6th spots. Karts in the 7th and 8th spots will usually wind up with Spiny Shells or Thunderbolts if they would've gotten a Special Items. Characters near the lead will rarely get anything better than a Red Shell, and will most often get Bananas, Fake Items, and Green Shells.

Banana

Characters: All
Forwards/Backwards: Yes!!

You're going to see a lot of Bananas on the tracks as you proceed through any of the given cups: of all of the items that you can get from an item cube, Bananas seem to be the most likely to pop up, especially when you're in or near the lead.

Bananas are used much like any other immobile item; try to plop them down where there's maximum traffic, or where your followers will be unable to avoid it, and you're sure to see someone slide out before long. As with the other immobiles, though, you have to be careful not to hit it yourself on the next lap. If you're coming up on a Banana without any means of avoidance, your best bet is to charge through; Bananas have the smallest speed penalty of any item, so you won't lost more than a second or two if you get back to top speed quickly.

Birdo's Egg

Characters: Birdo
Forwards/Backwards: Yes!!

We're trying very hard not to think about how Birdo creates all of these Eggs. Suffice to say, her Egg acts something like a Red Shell, in that it homes in on a character and knocks them over. Unlike the Red Shell, though, Eggs burst upon impact, spilling out three random items onto the track. These can sometimes be advantageous items, like Mushrooms, but are more often things like Bananas or Green Shells. As with Red Shells, you can prevent the impact of an Egg with a well-timed Shell directed towards your rear.

Bob-omb

Characters: Wario / Waluigi
Forwards/Backwards: Yes!!

The two W's get a rather explosive special item in the form of Bob-ombs, which are probably the most powerful item in the game in terms of sheer destructive force. After a Bob-omb is thrown forwards or backwards, it will sit for a few seconds, then begin to flash red and explode. The radius of the explosion is usually going to be sufficient to cover most of the track, if the Bob-omb was well-placed, and anyone hitting it will be propelled straight up into the air and will lose a significant amount of time. While these can be thrown forwards and backwards, Wario and Waluigi should be extremely careful when throwing them forward; it's all too easy to run right into your own trap.

Bowser's Shell

Characters: Bowser / Bowser Jr.
Forwards/Backwards: Yes!!

Bowser's Shell is, essentially, a larger and more powerful Green Shell, in that it heads off in a straight line, bouncing off of cars or barriers, tumbling anyone it comes into contact with. Unlike Green Shells, however, it isn't destroyed after its first enemy contact; if it hits someone, it'll pass through them, carving a path of destruction through every enemy in its way. It lasts a fair amount of time, as well, so be careful to keep an eye out for it when heading around corners; you may find yourself cut down by your own sword otherwise.

Chain Chomp

Characters: Baby Mario / Baby Luigi
Forwards/Backwards: No!!

The Chain Chomp can only be directed forward, which is understandable, considering that Baby Mario and Baby Luigi will be tethered to its rear end while it bursts ahead. When unleashed, the Chomp will grant the babies a speed boost, but will also steer for them for a short period of time, while knocking over any competitors that happen to be in the way. It's nice to have powerful friends.

Fake Item

Characters: All
Forwards/Backwards: Yes!!

As you get to know the tracks, you'll notice that item cubes always appear in the same spot if they're immobile, and stick to the same patterns of movement if they're mobile. Fake Items are easily detectable for this reason; if you spot an item cube in an odd place, or if you notice that there are two overlapping item cubes, avoid that spot, as you'll wind up losing your speed if you hit the Fake Item. Fake Items can also be detected via their reversed question mark, and the slightly reddish tinge they possess, but this shouldn't be necessary; their position should tell you instantly whether they're real or fake.