Super Mario 64/Secrets

MIPS the Rabbit
Once you've obtained 15 Power Stars, go down into the basement. If you explore it, you'll find a small, yellow rabbit, MIPS. If you get too close to him, he'll run off. If you can catch this quick rabbit, he'll ask you to let him go in exchange for a Power Star!

Once you've obtained 50 Power Stars, MIPS will re-appear in the basement, and if you catch him again, he'll give you a second Power Star!

The Castle Cannon, Roof, and Yoshi's Reward
If you explore the courtyard outside Peach's Castle, you'll find a closed-up cannon. Unlike the other cannons you'll find, this one is special. It will only open if you restore the castle's Star Power completely. In order to do that, you need to obtain every last Power Star in the game, a whopping 120! Once you've collected all of them, the cannon will open. When it does, hop into it and aim it at the castle roof. If you land on the roof, you'll find 3 1-Up Mushrooms, and none other than Yoshi! If you talk to him, he'll compliment you on your achievement, and give you a present from the Super Mario 64 Staff! You'll be given 100 Lives, and your Triple Jump will change so that you never get hurt! Unfortunately, if you save the game and turn it off, both your super triple jump and your 100-life upgrade will be gone, but Yoshi will be back!

The Big Penguin Became Fat!
Once you've obtained all 120 Power Stars, go into Cool, Cool Mountain and race the big penguin. However, you'll be in for a surprise: he's gotten fat! You can still race him, only he's bigger and harder. You won't get anything for the race, except for the shock that the big penguin decided not to slide for a while and let himself go!

Compliments from Bowser Himself
If you defeat Bowser in the final level after you've obtained all 120 Power Stars, he'll insult his troops for handing over all the Power Stars, and compliment you on your work to get them all, even the secret ones he missed!

Adjusting the Water Level in Wet-Dry World
Depending upon where you jump into the painting that leads to Wet-Dry world, the water level will raise or lower to that point. This way, you can reach the Bob-omb Buddy in the level by jumping into the highest area of the painting.

Secret Slide in Tall, Tall Mountain
After you pass by the cloud Fwoosh on Tall, Tall Mountain, you'll find a ledge with five coins on it. To the left of them is a painting hidden on the wall.

Jump into it to enter the secret slide! If you can make it past the twisted curves, avoid the dead-end on the slide, and make all the way to the end of the slide, you'll reach a portal that leads to another Power Star!

Big or Small
There are two paintings you can enter that will allow you to enter Tiny-Huge island tiny-sized or giant-sized. The one on the left makes you huge, and the one on the right makes you tiny.

Shortcut on Tiny-Huge Island
If you enter Tiny-Huge Island as a giant, swim over to the island with the ! Block on it at the start of the level. Line yourself up almost against the wall and parallel to the ! Block and do a Backwards Somersault. If you did it correctly, you should end up on top of the ! Block and be able to hop onto the top of the island in a big shortcut.

Odd Timing
There is a secret to how the Tick Tock Clock's mechanisms behave. Watch the position of the big hand on the grandfather clock before you enter the level!

...the clock's mechanisms will move at a slow, steady, and predictable pace, making the clock easier to navigate.
 * If the big hand is on 3...

...the clock's mechanisms will be moving at unpredictable speeds, making going up the clock wacky and hard. Sometimes, the mechanisms will even reverse!
 * If the big hand is on 6...

...the clock's mechanisms will move at a fast and frenzied but still predictable pace, making the clock harder to but still possible to go up.
 * If the big hand is on 9...

...the clock's mechanisms will come to a complete halt, and be stopped the entire time you're in the clock. This makes the clock very easy to traverse, but makes it a challenge to reach the very top of the clock.
 * If the big hand is on 12...

Secret Warp Points
Some courses have secret warp points that will take you to hidden areas in a level. They can be hidden in the most unexpected places, and you never know when you may trigger one. For example, In the Bob-omb Battlefield level, in the field with the Cannon in, Walk into the center of the flowers and you'll be teleported.

In Tiny-huge Island, after pressing purple switch, and running to the floating platform, one corner teleports you back.

Butterfly Rewards
In some courses, three butterflies may appear. If they do appear, try to catch one. One holds a hidden 1-Up Mushroom, while the other two conceal cannonballs.

If a whole group appears, don't bother with them because they hide nothing.