100% Completion

100% Completion refers to having mastered all aspects of a title. The Permanently Missable Items article is useful to those undertaking this challenge. Like the Three Heart Challenge and Speed Runs, 100% Completions are an optional challenge for The Legend of Zelda series fans.

To brag of having a 100% Completed file, one must have all Heart Containers, Weapon upgrades, Items, and Collectible items such as Ship Parts. Unlike other gaming series like Metroid or some Mario games, the Legend of Zelda series thus far has no in-game rewards (such as alternative or lengthened endings for the feat) or even bragging rights rewards that acknowledge the completion. Although finding every last collectible is difficult in its own rights, doing so makes gameplay easier than Speedruns, Minimal Completions, and Three Hearts Challenges.

General
The following tasks apply for every installment in the series. Checklist
 * Beating the game.
 * Collecting the map and the compass in every dungeon where they're available.

The Legend of Zelda
Most Difficult Aspect- Beating the game Checklist
 * 16 Heart Containers.
 * Both Bomb Capacity Upgrades.
 * Boomerang upgraded.
 * Magical Sword obtained.
 * Arrows upgraded to Silver Arrows.
 * Blue and Red Rings obtained.
 * Shield upgraded to Larger Shield.
 * All Dungeon Items Obtained.
 * Complete both Quests.

The Adventure of Link
Most Difficult Aspect- Beating the game Checklist
 * All 4 Heart Containers.
 * All 4 Magic upgrades.
 * Level 8 Life experience.
 * Level 8 Magic experience.
 * Level 8 Attack experience.
 * All 1-Up Dolls.
 * All spells.
 * Upward and downward stab attacks.

A Link to the Past
Most Difficult Aspect- Beating the game Checklist
 * All 24 Pieces of Heart found.
 * All four bottles obtained.
 * All items obtained.
 * Red Boomerang obtained.
 * Master Sword tempered to level 4.
 * Red Mail obtained.
 * Magic Meter halved.
 * Bomb and Arrow carrying capacity maxed.

Gameboy Advance remake (The Gameboy Advance remake included several new features, extending the checklist)
 * Four Swords completed.
 * Palace of the Four Sword completed.
 * Lumberjack sidequest completed.

Link's Awakening
Most Difficult Aspect- This is a matter of personal opinion. Checklist
 * All 12 Pieces of Heart found.
 * Trading Sequence completed (culminating with the Boomerang).
 * Sword upgraded to level 2 (Seashell Sword).
 * Magic Powder carrying capacity upgraded to 40 units.
 * Bomb carrying capacity upgraded to 60 units.
 * Arrow carrying capacity upgraded to 60 units.

Link's Awakening DX

 * In addition to those above …
 * Photography sidequest completed (many photographs are permanently missable).
 * Completion of the Color Dungeon.

Ocarina of Time
Most Difficult Aspect- One of the Deku Nut upgrades is permanently lost if it's not earned before collecting the Poacher's Saw. Because of this, the Mask Trading Sequence must be done before proceeding further on the Biggoron's Sword sequence (this is fixed in Ocarina of Time 3D). Checklist
 * All 36 Pieces of Heart found.
 * First four Happy Masks sold (with the availability of the other four masks being the reward).
 * All upgrades (Deku Nuts and Bombs up to 40, Deku Sticks up to 30, Arrows and Deku Seeds up to 50, Rupees up to 500, and the Golden Scale and Golden Gauntlets).
 * Equipment complete (including the Biggoron's Sword).
 * All Skulltulas killed, receiving the rewards (and, although optional, receiving a Huge Rupee after talking to the last cursed man as thanks).
 * All four bottles.
 * All items (including the Ice Arrows).
 * Retrieving Epona, having the cow from Lon Lon Ranch in Link's house after winning Malon's racing minigame.
 * Racing the running man from Gerudo Valley at least once (as it saves the time record inside the list of greatest deeds at Link's house).
 * Catching the Hylian Loach.

Majora's Mask
Most Difficult Aspect- Keeping an eye for time-sensitive events, particularly those that are mutually-exclusive. Checklist
 * All 52 Pieces of Heart found.
 * Collecting the Fierce Deity's Mask (which provides that all other masks were found as well).
 * All six bottles.
 * Bomber's Notebook complete.
 * All Stray Fairies rescued (and the rewards received).
 * Sword tempered with Gold Dust, Mirror Shield obtained.
 * All upgrades (Bombs up to 40, Arrows up to 50, Rupees up to 500).
 * All of Tingle's maps purchased, and therefore the map of Termina fully visible.
 * All Owl Statues activated.

Oracle of Ages
Checklist
 * All 12 Pieces of Heart
 * All 8 heart containers (9 heart containers in a linked game)
 * All 32 rings (only in a linked game)
 * L-2 Sword (or L-3 in a linked game)
 * L-2 Shield (L-3 shield in a linked game)
 * 30 bomb upgrade (50 bomb upgrade in a linked game)
 * 50 seed upgrade (99 seed upgrade in a linked game)
 * L-2 ring box (L-3 ring box in a linked game)
 * Biggoron Sword (only in a linked game)
 * Bombchus (only in a linked game)
 * Veran defeated

Oracle of Seasons
Checklist
 * All 12 Pieces of Heart
 * All 8 heart containers (9 heart containers in a linked game)
 * All 32 rings (only in a linked game)
 * L-2 Sword (or L-3 in a linked game)
 * L-2 Shield (L-3 shield in a linked game)
 * 30 bomb upgrade (50 bomb upgrade in a linked game)
 * 50 seed upgrade (99 seed upgrade in a linked game)
 * L-2 ring box (L-3 ring box in a linked game)
 * Biggoron Sword (only in a linked game)
 * Bombchus (only in a linked game)
 * Onyx defeated

The Wind Waker
Most Difficult Aspect- Completing succesfully the Nintendo Gallery, due to some of the figurines being of ephimeral availability. Checklist
 * All 44 Pieces of Heart found.
 * All 61 Charts collected (and, in the case of the 41 Treasure Charts, all treasures must have been collected).
 * All four bottles.
 * All upgrades (Bombs and Arrows up to 99, Rupees up to 5000).
 * Hero's Charm and Magic Armor collected.
 * All 12 possible souvenirs obtained in the trading sequence available at Zunari's Shop.
 * All three types of potion prepared in Doc Bandam's shop.
 * All memberships gained in Beedle's Shop Ship.
 * Nintendo Gallery complete.

The Minish Cap
Checklist
 * 100 Kinstone Fusions (and Kinstone Bag converted to Tingle Trophy)
 * 44 Pieces of Heart found
 * Full Heart Container found
 * All 4 bottles obtained (requires completion of Goron Sidequest)
 * All 8 Golden Monsters defeated
 * All 136 figurines obtained
 * Magical Boomerang obtained
 * Mirror Shield obtained (requires completion of Goron Sidequest)
 * Bomb carrying capacity upgraded
 * Remote bombs
 * Arrow carrying capacity upgraded
 * Light Arrows
 * All 8 Tiger Scrolls obtained
 * All 4 Sword Technique upgrades obtained
 * Wallet capacity upgraded to 999 rupees
 * Homes found for 2 of Din, Nayru and Farore
 * All 3 Joy Butterflies found
 * All 8 Swordsman Newsletters
 * All 6 colours of Picolyte made available

Twilight Princess
Most Difficult Aspect- This is a matter of personal opinion. Checklist
 * All 45 Pieces of Heart.
 * All upgrades (three Bomb Bags plus the Big Bomb Bag that doubles the capacity of the bombs currently stored; arrows up to 100, Rupees up to 1000).
 * All four bottles.
 * All 24 Golden Bugs collected.
 * All 60 Poes captured (and, although optional, receiving 200 Rupess from Jovani, talking to him in the bar and then receiving 200 Rupees from his cat at least once).
 * Equipment complete (including the Magic Armor).
 * All seven Hidden Skills learned.
 * All types of fish captured.
 * Level 8-8 of Rollgoal completed.
 * Fully completing the Cave of Ordeals.
 * Sinking lure found.

Phantom Hourglass
Most Difficult Aspect- Collecting enough money to purchase the upgrades for sale, getting the (random-appearing) Ship Parts. Checklist
 * All 13 extra Heart Containers.
 * All 20 Power Gems, all 20 Wisdom Gems, and all 20 Courage Gems.
 * All 35 Charts (including the four vital Sea Charts) collected, and their respective treasures retrieved.
 * All upgrades (Bombchus and Bombs up to 30, arrows up to 50).
 * Great Spin Attack learned.
 * All Ship Parts collected.
 * All memberships from Beedle gained.
 * 25-minute-worthy Sand of Hours.

Spirit Tracks
Most Difficult Aspect- Collecting the indicated treasures for the Train Cars. Checklist
 * All 13 extra Heart Containers.
 * All upgrades (Bombs up to 30, arrows up to 50).
 * Both Swordsman's Scrolls, which proves that:
 * All 50 rabbits have been captured.
 * The Stamp Book has been completed.
 * The Spirit Tracks fully restored.
 * All stations visited and beaten.
 * All Train Cars collected.
 * All memberships from Beedle gained.