Credit for this list goes to DragonEyez, Kife, and special thanks to any others who helped along the way. Finalization and grammar editing done by me.
Dragon Scale
What it does: Powers Up Dragon
Pokemon(s) that hold this item:
Horsea (You can Find it at Cold Cavern)
Spell Tag
What it does: Powers Up Ghost
Pokemon(s) that hold this item:
Shuppet (You can Find it at Dark Cave)
Duskull (You can Find it at Memorial Cave)
Kings Rock
What it does: Flinch + Evolve
Pokemon(s) that hold this item:
Teddiursa (You can Find it at Memorial Cave)
Metal Coat
What it does: Powers Up Steel + Evolve
Pokemon(s) that hold this item:
Magnemite (You can Find it at Victory Path)
Poison Barb
What it does: Powers Up Poison
(Now Unobtainable)
Soft Sand
What it does: Powers Up Ground
Pokemon(s) that hold this item:
Trapinch (You can Find it at Meteor Hills)
Leftovers
What it does: HP Restoration
Pokemon(s) that hold this item:
Spheal (You can Find it at Dark Islands)
Sharp Beak
What it does: Powers Up Flying
Pokemon(s) that hold this item:
Doduo (You can Find it at Empty Cliffs)
Pidgey (You can Find it at Empty Cliffs)
Miracle Seed
What it does: Powers Up Grass
Pokemon(s) that hold this item:
Oddish (You can Find it at Empty Cliffs, Hidden Cove and Safari Zone)
Silver Powder
What it does: Powers Up Bug
Pokemon(s) that hold this item:
Heracross (You can Find it at Hidden Cove)
Darkglasses
What it does: Powers Up Dark + Evolve
Pokemon(s) that hold this item:
Poochyena (You can Find it at Dark Cave)
Pink Bow
What it does: Powers Up Normal
Pokemon(s) that hold this item:
Phanpy (You can Find it at Dark Cave)
Polkadot Bow
What it does: Powers Up Normal
Pokemon(s) that hold this item:
Whismur (You can Find it at Meteor Hills)
Exp Share
What it does: Shares exp earned with the pokemon you attached the item to.
Pokemon(s) that hold this item:
Wobbuffet (You can Find it at Victory Path)
Magnet
What it does: Powers Up Electric
Pokemon(s) that hold this item:
Pikachu (You can Find it at Victory Path and Untouched Growth)
Scope Lens
What it does: Critical hit 3/5 of the time in which you attack.
Pokemon(s) that hold this item:
Absol (By Regiquest)
Charcoal
What it does: Powers Up Fire
Pokemon(s) that hold this item:
Vulpix (You can Find it at Meteor Hills and Untouched Growth)
Twisted Spoon
What it does: Powers Up Psychic + Evolve
Pokemon(s) that hold this item:
Abra (You can Find it at Untouched Growth)
Spoink (You can Find it at Victory Path)
Hard Stone
What it does: Powers Up Rock
Pokemon(s) that hold this item:
Aron (You can Find it at Dark Cave)
Upgrade
What it does: Evolves Porygon2 into PorygonZ
Pokemon(s) that hold this item:
Porygon (You can Find it at Victory Path)
Silph Scope
Defeat the Silph Co. Only a 10% chance to obtain it.
What it does: Unlocks the full Lavender Tower.
Here's the Link to Silph Co. --->
http://tppcrpg.net/battle.php?Battle=SilphCo
Team Boost
What it does: Increases faction gains to 4500 points and 9000 if your opponent Has more team points than you.
Where to get it: Trading in Team Stat points.
Rank: Private
Amulet Coin
What it does: Doubles cash earned after a battle.
Note: The pokemon who is out when the opponent faints has to have the coin attached.
Where to get it: Trading in Team Stat points.
Rank: Specialist
Power Boost
What it does: Makes moves do 10% more damage. (Toxic/etc don't count)
Where to get it: Trading in Team Stat points.
Rank: Captain
Elemental Stone
What it does: Makes moves do 50% more damage. (Toxic/etc don't count) and increases your chance of critical hit to 4/5.
Where to get it: Trading in Team Stat points.
Rank: Colonel
Rare Metal
What it does: (See 'How to use it')
How to use it: 6 Rare Metals attached on your roster set + a specific pokemon as your starting pokemon + evolution gym unlocks Twilight Orb or Twilight Rod.
Where to get it: Defeating the Unown Tower in Battle Towers.
Twilight Orb
What it does: Unlocks Unown Tower Phase #1.
Where to get it: From rare metals + Fire pokemon + Evolution gym.
How to unlock phase: Just have your starting pokemon with the item attached and go to the Unown Tower.
Twilight Rod
What it does: Unlocks Unown Tower Phase #2.
Where to get it: From rare metals + Steel pokemon + Evolution gym.
How to unlock phase: Just have your starting pokemon with the item attached and go to the Unown Tower.
Twilight Rod + Twilight Orb
What it does: Unlocks Unown Tower Phase #3.
How to unlock phase: Just have your starting first two pokemon with the item attached and go to the Unown Tower.
Rough Diamond
What it does: Unlock Smooth Diamond
How to use: Have a fire Pokemon as your starter and bring 10 Rough Diamonds to the Research Lab and trade it in.
Pokemon(s) that hold this item:
Every one on Maps.
Rough Pearl
What it does: Unlock Smooth Pearl
How to use: Have a water Pokemon as your starter and bring 10 Rough Pearls to the Research Lab and trade it in.
Pokemon(s) that hold this item:
Every one on Maps.
Smooth Diamond
What it does: Evolves Electabuzz into Electivire.
Where to get it: See (Rough Diamond).
Smooth Pearl
What it does: Evolves Magmar into Magmortar.
Where to get it: See (Rough Pearl).
X Special
What it does: Boosts Special Attack
Pokemon(s) that hold this item:
Articuno (See 'Sapphire Shard')
X Defense
What it does: Boosts Defense
Pokemon(s) that hold this item:
Moltres (See 'Ruby Shard')
X Attack
What it does: Boosts Attack
Pokemon(s) that hold this item:
Zapdos (See 'Emerald Shard')
X Accuracy
What it does: Boosts Accuracy
Pokemon(s) that hold this item:
Kecleon (You can Find it at Tree Path and Memorial Caves)
X Speed
What it does: Boosts Speed
Pokemon(s) that hold this item:
Voltorb (You can Find it at Untouched Growth)
Note:
When attached, X Special (Attack), Attack, Defense, and Speed add 20 points to your base stat in that category, meaning that your move will do more damage.
X Accuracy makes whatever move you're using 10% more accurate. This includes OHKO moves in addition to all the other moves in the RPG.
Mystic Water
What it does: Boosts Water Attacks + Evolve
How to get it: 1st-5th Place in Seafoam Islands - Magikarp Cup
(Now Unobtainable)
Focus Band
What it does: May prevent Pokemon from fainting (really small chance).
How to get it: 1st Place in Seafoam Islands - Gyarados Cup
(Now Unobtainable)
New
Items:
Charge Rod
What it does: Currently Unknown.
Where to get it: Trading in Team Stat points.(If your Team Wins in the Power Plant).
Rank: Grunt
Scrap Metal
What it does: Currently Unknown.
Where to get it: By over used of Charge Rod
Life Orb
What it does: It increases attack power at the cost of some HP.
Where to get it: Trading in Team Stat points.
Rank: Sergeant
Alph Glyph
What it does: To Find Shiny/Dark Unknown in Caverns of Alph (You must Attach the Alph Glyph to your starter)
Where to get it: Trading in Team Stat points.
Rank: Lieutenant
Valor Band
What it does: To Find Azelf (You Must attach the Valor Band to your starter and go to the map and find them at the bottom of the page)
Where to get it: Trading in Team Stat points.
Rank: Major
Team: Galactic
Magma Stone
What it does: To Find Heatran (You Must attach the Magma Stone to your starter and go to the map and find them at the bottom of the page)
Where to get it: Trading in Team Stat points.
Rank: Major
Team: Magma
Verity Stone
What it does: To Find Mesprit (You Must attach the Verity Stone to your starter and go to the map and find them at the bottom of the page)
Where to get it: Trading in Team Stat points.
Rank: Major
Team: Rocket
Acuity Water
What it does: To Find Uxie (You Must attach the Acuity Water to your starter and go to the map and find them at the bottom of the page)
Where to get it: Trading in Team Stat points.
Rank: Major
Team:TPPC
DNA Strand
What it does: To Find Deoxys (You Must attach the DNA Strand to your starter and go to the map and find them at the bottom of the page)
Where to get it: Trading in Team Stat points.
Rank: Major
Team: Aqua
NeverMeltice
What it does: Evolves Eevee into Glaceon.
Pokemon(s) that hold this item:
Jynx (You can find at Cold Caverns and Frozen Ruins)
Small Charm
What it does: To Get a Phione
Obtain it by completing 20% of your Pokedex. If you attach it to your starter Pokemon and beat the Baby Tower, you'll receive Phione.
Ruby Fragments
Pokemon(s) that hold this item:
Every one on Maps.
Sapphire Fragments
Pokemon(s) that hold this item:
Every one on Maps.
Emerald Fragments
Pokemon(s) that hold this item:
Every one on Maps.
Ruby Shard
What it does: To Find Moltres
Where to get it: You Must Find 10 Ruby fragments and convert them at the Research Lab.
Sapphire Shard
What it does: To Find Articuno
Where to get it: You Must Find 10 Sapphire Fragments and convert them at the Research Lab.
Emerald Shard
What it does: To Find Zapdos
Where to get it: You Must Find 10 Emerald Fragments and convert them at the Research Lab.
Secret Key
Where to get it: You need to battle the Team Rocket Grunt on Monday and Thursday at the Radio Tower in order to obtain it. Attach the Secret Key to your starter Pokemon and start clicking around Map 1 (Dark Islands) until you come across a message that tells you to enter some sort of Secret Passage. Click that link.
Gracidea
Where to get it: After you beat Shaymin, you get another item (The Gracidea). Attach THAT to your starter, click around the maps until you find a Shaymin, beat it, and then it's added to your box.
Griseous Orb
Where to get it: Search the Caverns of Alph map while Giratina is in your first slot. You will see a yellow object on the map; click it and defeat the Giratina to obtain the Griseous Orb. Attach it to Giratina and beat the Evolution Gym in order for Giratina to change into Origin form.
Quick Claw
Pokemon(s) that hold this item:
Meowth (you can find at Memorial Caves)
Azure Flute
What it does: Lets you unlock Arceus battle.
How to use it: Obtain 6 Azure Flutes and search on the map called Empty Cliff, a researcher will pop up on the map, and he will take you to the Arceus battle where you have to beat all 17 forms of Arceus to win an Arceus.
Where to get it: Having one ShinyPalkia, one ShinyDialga, and one Giratina in your team, keep clicking on the Ancient Temple map until a researcher shows up. Beat him and you will have a chance of obtaining an Azure Flute
Note: after you win Arceus, the Azure Flutes break.
Guides Gone Wild
