There are quite a few of them. Try them out: In Verbal Assualt say "Bullet Bills" to have Bullet Bills attack your opponents or "Goomba" to shoot them with Goombas. In Shoot Your Mouth Off, cause extra damage to your opponents by saying "Zero" which drops Thwomps on their heads.
To unlock Fire Run for the Star Sprint, you must buy it from the star bank for 50 stars.
To be able to play in Clockwork Tower, you must buy it for 100 stars.
Here's a little secret. Some minigames are based on the board you're playing on.
Example: The Snowboard minigame is most likely to appear in Snowflake Lake.
When youplay Mic, Solo, or Party mode, their seems to be a blank person on Character Select. Fortunately for you, you can buy the person. The Character is Toadette, Toad's sister or girlfriend, all I know is they know each other. Save up 30 stars to buy Toadette, a girl version of Toad who is addicted to Sluggish 'Shroom Capsules.
You can buy Seer Terror, a surprise from Bowser, for 50 stars.
Here are all the effects of Mushrooms in the Game.
Mushroom~ Allows you to hit the dice 2 times. Golden Mushroom~ Allows you to hit the dice 3 times. Sluggish 'Shroom~ Slows down the dice so you can hit a specific number. Metal Mushroom~ Turns you to metal and effects of opponents traps don't affect you.