The Legend of Zelda: Ocarina of Time/Secrets

Giant enemies
If you repeatedly kill some types of enemy within a short period a giant version will appear. This applies most to the Stalchildren running rampant during the night on Hyrule Field, the Guay located at Lon Lon Ranch and the Leevers at Desert Colossus (in which case actually change colour from green to purple).

Dungeon Map
When you get a dungeon map from a treasure chest, the item that Link holds displays the map for the first floor of Dodongo's Cavern.

Power Stab
If you hold hold down and press, Link will stab with his sword. However, the power of the stab varies depending on the attack you used immediately before the stab — if you jump-attacked with a Deku Stick then stabbed (without using any other sword attacks), that stab will have the power of the Deku Stick jump attack. This is useful for getting the power of the Deku Stick without wasting your Deku Sticks. This works with any sword attack, Deku Stick attacks, and the Megaton Hammer.

Never lose tunics and shields
When a Like-Like is eating you, equip the Kokiri Tunic and Mirror Shield. Because neither can be purchased, nothing in the environment is able to destroy them, and so the Like-Like can't eat them.

Free money
As Young Link, travel to the drawbridge from the field in front of Hyrule Castle Town. Walk straight up the chain until your face appears to be in the wall then turn towards the middle and jump down. You'll get 20 rupees while you're falling and enter Hyrule Castle Town.
 * Hyrule Castle's drawbridge (20 rupees during the day, and 80 when the gate closes at night)

If you decide to wait until night, climb up and stand on either chain. After the drawbridge raises, walk across the narrow end of the upturned drawbridge to collect 80 rupees (four red ones).

For more free money, go into the hole behind the potion shop in Kakariko Village. Catch a bug in a bottle, and then go back to where the very tall ladder is. Look for the begger who will buy items assigned to C buttons, and sell him the bug. He will give you 50 rupees. You can do this as many times as you want.
 * Kakariko Village (50 rupees)

200 Rupees
This trick requires Adult Link, the Biggoron's Sword (although not needed, it will make defeating him much easier because with the master sword it takes 5-6 strikes to defeat him), and (preferably, although not required) the Giant's Wallet. Enter the Lost Woods and turn left. There should be a Skull Kid standing on top of a tree stump. Approach him, and when he advances on you, quickly attack him with the Biggoron's Sword, using the stabbing-motion (forward+B). If you are able to defeat him before he disappears, you'll be rewarded with a special rupee, so big that it will fill any wallet you have, even the Giant's!

A similar reward can be achieved with the help of the Bunny Hood, which Young Link can obtain from the Happy Mask Shop once he has already sold the Keaton Mask, Skull Mask, and Spooky Mask. Once you've got the Bunny Hood, go to Hyrule Field, approaching Lon Lon Ranch. You should eventually see a man running laps around the ranch. If you wear the Bunny Hood and speak to him, he will ask you to sell it to him. Say yes and he'll pay you five hundred Rupees. It is preferable that you have the Giant's Wallet for this, otherwise you won't receive as much as you could.

Fish Money
As grown-up Link go to Kakariko Village enter the hole behind the old lady's potion shop (the one inside the high fenced area). Capture a fish in a bottle, then show it to the crazy beggar guy — he will buy it from you for 100 rupees.

30 quick Kokiri Forest rupees, as a kid
As young Link, when first starting out, this helps you to get the Deku Shield faster. Go into the Kokiri shop, go the empty space to the right, and walk behind it. There you'll get a red rupee (20).

Jump across the stepping stones that lead to the Deku Tree. As you hop over the last one, it will give you a blue rupee (5).

At the training ground, where you go to find the Kokiri sword, you'll see a gate in front of the Know-It-All Brothers' place. Turn left and there will be a sign. Destroy the sign and claim the blue rupee (5) that pops out.

200 rupees, in Kakariko village, as a kid
This is easier to find if you have the Rumble Pak and Stone of Agony. Enter Kakariko Village, and run up to where the house of Skulltula is, walk up, and walk around the area. Feel the rumble? Bomb the spot where you feel the rumbling. A hole will appear. Fall down the hole. You will now see two ReDeads. Play the Sun's Song to freeze them. Then defeat them by slashing away at them with your sword. After you defeat both of them, a treasure chest will appear. Open the chest, and claim the 200 rupees inside.

Unlimited Rupees
Once you get all 100 Gold Skulltula coins, simply return to the last family member to receive a gold rupee. You can just leave the house and go back in to get another.

Gossip Stones
Attacking the Gossip Stones in various manners has a useful purpose outside of entertainment value: by playing Zelda's Lullaby in front of one, a fairy will emerge. Bombing a Gossip Stone will cause it to flash blue and red and take off after a few seconds. Hitting one with your Megaton Hammer will flatten it temporarily. Even comparatively boring attacks, such as with a sword or a hookshot, cause the stone to vibrate differently, depending on the weapon used.

Chicken Attack
Note: this is a rather dangerous (though quite amusing) pursuit, so do not attempt it if your health is low — one hit from a chicken depletes an entire heart container. If you are inclined to be attacked by an enormous horde of chickens, attack one repeatedly until it calls up its buddies, and then run as rapidly as possible in the opposite direction (zig-zag as you run). Two of the better places to do this are at the entrance to Kakariko Village, where there is an easy escape route, or in Lon Lon Ranch, where you can attack them while riding Epona and be invincible to their attacks. Note: Megaton Hammer will work with one attack because it is hitting multiple times with one attack.

Sign Reconstruction
If you ever feel the need to take out your aggression on one of the larger wooden signs with a sword or bomb and subsequently realize that you actually wanted to read it, either leave the room or play Zelda's Lullaby and watch the sign put itself back together.

Crossover Crisis for 20 rupees
There is one crossover in this game: when you first meet Zelda in the castle. If you look in the last window on the right, you can see a picture of a certain famous red-clad plumber and some of his friends. Shoot the picture with the slingshot to get a red rupee.

Stabbing the Cursed Ones
You can actually attack the cursed family in the House of Skulltula just like you do with a regular skulltula. First, wait for one of the family members to drop down, then hit them in the front with your sword. While they're swinging back and forth, quickly run behind them and attack their backside. They will let out a high-pitched scream and be frozen. Eventually they will come to and return the favor, by attacking back, so it's wise to keep your distance.

Stone of Agony
To really find all the secrets around Hyrule, you'll need some help. Luckily, if you acquire 20 Gold Skulltulas you can go to the House of Skulltula in Kakariko village to get the reward, the Stone of Agony, from the person who has been most recently freed from the curse. The Stone of Agony is a rumble pack-shaped passive item that makes your controller vibrate when close to a hole in the ground. When close to one of these holes, you'll have to figure out the special way to open it (bombs, a certain song on the Ocarina, etc.).

If you don't have a rumble pack for the N64 or have the rumble feature turned off, the Stone of Agony will be of no use. Note that the rumble feature is stripped from the Wii version, leaving this quest item useless.

A Daytime Dog Companion
If you get a dog to follow you in Hyrule Market at night, you can play the Sun's Song and he'll still be right beside you in the daytime. However, if you run away and the dog goes offscreen, he'll vanish.

Wolfos Treasure Den
At the entrance to the Sacred Forest Meadow, if you have a Rumble Pak and the Stone of Agony, you may feel your controller vibrate. Drop a bomb near that spot, and a hole should open. Inside are two Wolfos. Defeat them, and you'll reveal a chest with a Purple Rupee.

Mario Referance
At Hyrule Castle, goto where Zelda is and look at one of her windows, there will be pictures of Mario and Bowser.