Super Mario 64/Secrets

Fall and take no damage
If you fall too far, you will lose some health. If you ground pound right before you touch the ground (or fall too far), you will take no damage.

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.

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. The secret warp points are:
 * In ../Whomp's Fortress/, at the first Thwomp, walk to the Metal Cap Block and walk a little farther. It will teleport you to the "observation area" near the top of the fortress. This is a shortcut to Star 2, To The Top Of The Fortress.
 * In ../Tiny-Huge Island/, after pressing the red switch and running to the floating platform, the corner with a single coin teleports you back.
 * There are two on Bob-omb Battlefield, one to the right of the wooden bridge at the start, near where Koopa the Quick is after you race him. If you stand in the flower garden you will be warped over to the field where the water bubbles are being shot. The second one is in the cannon holes going up the mountain; if you press against the back wall of the first one, you will be teleported to the second. This can help during the race with Koopa the Quick.
 * Cool, Cool Mountain: from the start of the level head right and get as close to the corner of the slope and cliff as you can, and you will be teleported to the broken bridge near the penguin looking for her baby.
 * Tall, Tall Mountain: go to the Scary 'Shrooms area. On one of the shrooms, there is a warp that takes you to the cannon.
 * Rainbow Ride: there's one on the doorstep of the house. Just climb the stairs and stand outside and it will warp you to the top of the red coin area by the ! block.
 * There are two more in the Pyramid Level: standing next to the 1-Up palm tree on the water side will transport you to the wing cap near the cannon. The other is inside the Pyramid near the rolling thwomp thing near the pole and takes you to the 1-up on top of the cage.
 * The warp point in Lethal Lava Land is located in the middle of the island toward the beginning with the wing cap. This takes you in the pocket beneath the closest eye. This is more useful to return to the wing cap after making the eye roll.

Floating Penguin
Enter ../Cool, Cool Mountain/ in the Lil' Penguin Lost level. Bring the baby penguin at the beginning to the mother penguin at the end and grab it again. Jump into the star while still holding the penguin and voila, the penguin is floating.

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 three 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 101 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 101-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!

Secret Star on Secret Slide
Go to The Princess's Secret Slide. Go as fast as you can, because if you reach the bottom of the slide in under 21 seconds, you'll get another star!

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!

Secret Slide in Tall, Tall Mountain
Once you can see the black brick behind the waterfall, long jump to the low ledge. After you pass by the cloud Fwoosh on ../Tall, Tall Mountain/, you'll find a ledge with five coins: to the left of them is a painting hidden on the wall. Jump into the painting 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, you'll reach a portal that leads to another Power Star!

L9: the changes in Dire, Dire Docks
If you return to ../Dire, Dire Docks/ after completing ../Bowser in the Fire Sea/, you will notice three changes:
 * 1) Bowser's Sub disappears. People have a theory that this happens because Bowser has left the fire sea and gone to the sky, and the ../Dire, Dire Docks/ portal is in the same room, so he takes his sub with him.
 * 2) Moving poles appear at the framework of the docks.
 * 3) The gate blocking the passageway to the pond outside Princess Peach's Castle is open.

L11: 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 rise or fall to that point. This way, you can reach the Bob-omb Buddy in the level by jumping into the highest area of the painting.

L13: small island or big island?
There are two paintings you can enter that will allow you to enter Tiny-Huge island on the tiny-sized island or the huge-sized island. The one on the left takes you to the tiny island, and the one on the right takes you to the huge island.

L13: shortcut on Tiny-Huge Island
If you enter Tiny-Huge Island from the left entrance, where everything is tiny, 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. You can also do the reverse direction back flip to achieve this, although it works better on the second platform with the Tube and Piranha Plant.

L14: 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...