Noble Sword:

While you are in the middle of the Lost Woods, you must change the season to winter, go left, change the season to fall, go left, change the season to spring, go left, change the season to summer,go left, and you should find the Noble Sword. This only works in Oracle of Seasons and NOT in Oracle of Ages. To get the sword in Oracle of Ages you must trade for the Old Zora's Broken Sword and get Patch to fix it.

Master Sword:

After you've beaten Oracle of Ages and are halfway through a password-linked Oracle of Seasons game. Go through Hero's Cave and talk to the Zora on a raised platform. He'll give you a password to take to King Zora in your saved Oracle of Ages game. He'll reward you with a sword upgrade. If you have the Wooden Sword, you will receive the Noble Sword. If you had the Noble Sword he will give you the Master Sword, the Lv.3 Sword. Afterwards he will give you a password to take to Farore in the Hall of Secrets in Oracle of Seasons (inside the big Maku Tree) to get that same sword upgrade.

Shield Power-up:

After you get the pirates to take you to the Holodrum graveyard, enter the house just to the left of the ship. Talk to the ghost to get a password. Then switch over to your Oracle of Ages game and tell the password to the man in the back of the Eyeglass Isle Library in the past of Labrynna. He'll give you a shield upgrade and a password to take to Farore in Oracle of Seasons.

Extra Heart:

Container Right after you talk to the Maku tree for the first time, you'll find a girl near fountain in the middle of Horon Village. She'll give you a password that you can take to the fairies in the Fairies Woods in the present. They'll give you another Heart Container and a password. Take that password to Farore in Oracle of Seasons to get that same Heart Container.

Upgrade From Bombs to Bombcus:

You'll notice that the man playing the music in the Woods of Winter has a single boy as an audience. He'll give you a password to take to Troy in present-day Labrynna of your saved Oracle of Ages game (he's in the Gorons' mine cart game where you have to shoot the blue crystals with your seed shooter). If you play a perfect round of the game, you'll get the bombchu, a homing bomb that locks onto the enemies. He'll tell you a password, too. (If you haven't looked at the previous codes, then you should take it to Farore in Oracle of Seasons.

Spin Ring:

The Spin Ring allows you to spin twice when you power up your sword. After you've acquired the power of autumn and gone to Lava Lake, you'll meet a Subrosian that'll give you a password that you can take to Mayor Plen of Lynna City. He'll give you the ring.

Snowshoe Ring:

The Snowshoe Ring stops you from sliding on ice. Talk to Mamamu Yan's mother in the Floodgate Keeper's House for a password. Take the password to Mamamu Yan. Win the minigame you will enter for the prize.

All The Power Rings:

The first power ring is in the Explorer's Crypt. The second one requires you to either plant a gasha seed in the desert, or in the middle-of-water area (you'll need either the flippers, or Dimitri), and fight up to 250 enemies. The last, power ring will require the "Gasha" ring (found by Maple). Equip that, and go to an area where unlimited monsters appear (oh yeah, plant the seed in the desert), fight them, for around 10-15 minutes, then leave. Unequip the Gasha ring and go to the Gasha plant, and you'll get it