Mario 64     

1,000 coin trick:  go to any Bowser and keeep running around him and
collect the coins that appear after his fire.  Once a 1,000 coins are had
from now on you'll gain a life everytime you die.  Beware though 1-ups
will subtract a life. 

Go up a slope: while sliding down a slope jump up and kick while pulling
back.  Repeat to go up. Water trick: when your low on health just find
some water and dive in and rest there till all your energy returns. 

No damage from falls: falling from the great hieghts in this game is
unavoidable.  So when you find yourself looking at the ground rushing
towards to your face ready to spread your inards all over the relm try
this.  Don't hit any buttons on your way to your demise. then watch your
shadow.  When the ground gets really close hit a button to do a dive or
whatever.  This'll make it so your not hurt and its pretty fun just to try
it out to make sure you can do it. 

Change Obstacle Speed: To change the obstacle speed on Course 14, try
this. For slower obstacles, enter when the minute hand is on 3. To stop
them completely, enter when the minute hand is on 12. 

Find Yoshi: Collect all 120 Stars. Go to the Castle Gardens. The grid near
the Fish Pond will open, revealing a cannon. Shoot yourself onto the roof
of the Castle and Yoshi will be there! 

Messed-up Room:  Get 120 stars and shoot yourself to the top of the roof
were Yoshi is. Then get the wings and fly to the highest ledge you can
stand on.Run up the wall and you should fall in the roof in to a messed up
room. This might take a few tries. 
Stretch Mario: Turn on the game. When you see Mario's face, hold all
buttons and use the d-pad or joystick to stretch Mario's features. To
maintain his warped features, hold the Right Trigger.