What are the Item restrictions during VS races?

In Mario Kart Wii, certain items have restrictions for when or under what condition they may be gotten. By this, I do not mean the items based on placement system.

Some Items can be pulled only after a certain time limit. For example, the Shock can be used only once in 30 seconds. I know there are other items that have similar use restrictions, but what are these items, and what restriction do they have?

Solution 1:

I'm not sure about other items with time restrictions. But I do know that some items are restricted to only one existing in a race at a time.

For example, only 1 blue shell can exist at any one time.
So if someone gets a blue shell from an item box, they could hold onto it the whole race, and no one would ever get a blue shell.

I believe Bullet Bill follows this rule too.
There's a good chance that there's a "cooldown" for bloopers/POW blocks too, as you never really see two of them at the same time, and they also hit multiple players at once.