Items are an integral part of Pokémon games and XD, like other games has a good batch of items. Here however I will only list the integral items...the Hold Items & Key Items. Any item not listed is not found naturally in the game:

Hold Items

Picture Name Effect Location
Amulet Coin Double Money is Earnt from Battles Gateon Port, Emma, after scaring Bonsly off from Deserted Cruiser Libra
Black Belt Any Fighting Type Move's Power is increased by 10% Shadow Hitmonlee
BlackGlasses Any Dark Type Move's Power is increased by 10% Shadow Carvanha
Charcoal Any Fire Type Move's Power is increased by 10% Shadow Numel
Dragon Fang Any Dragon Type Move's Power is increased by 10% Shadow Altaria
EXP. Share This Pokémon gets EXP from battle even if it isnt used Phenac Mayor Dagude
Hard Stone Any Rock Type Move's Power is increased by 10% Shadow Lunatone
Leftovers HP Increases by 1/16th each turn Shadow Snorlax / pick up at Deserted Cruiser Libra after Bonsly flees
Lucky Egg Pokémon this Item is attached to gets more EXP in battle Agate, Beluh, after removing all translators from Overworld Pokémon
Lucky Punch If attached to Chansey, Critical Hit Ratio Rises Shadow Chansey
Macho Brace Lowers Speed but increases Effort Values Prize for clearing Mt. Battle Area 1
Magnet Any Electric Type Move's Power is increased by 10% Shadow Voltorb
Metal Coat Any Steel Type Move's Power is increased by 10%. Evolves Onix & Scyther when traded Shadow Magneton
Miracle Seed Any Grass Type Move's Power is increased by 10% Shadow Tangela
Mystic Water Any Water Type Move's Power is increased by 10% Shadow Seel
NeverMeltIce Any Ice Type Move's Power is increased by 10% Shadow Swinub
Poison Barb Any Poison Type Move's Power is increased by 10% Shadow Beedrill
Sharp Beak Any Flying Type Move's Power is increased by 10% Shadow Spearow
Silk Scarf Any Normal Type Move's Power is increased by 10% Shadow Zangoose
Silverpowder Any Bug Type Move's Power is increased by 10% Shadow Venomoth
Soft Sand Any Ground Type Move's Power is increased by 10% Shadow Dugtrio
Soothe Bell Happiness Level Raises Easier Receive from mother of lost girl in ONBS
Spell Tag Any Ghost Type Move's Power is increased by 10% Shadow Banette
Stick If attached to Farfetch'd, Critical Hit Ratio Rises Shadow Farfetch’d
Thick Club If attached to Cubone or Marowak, their Attack rises by 100% Shadow Marowak
TwistedSpoon Any Psychic Type Move's Power is increased by 10% Shadow Ralts

Obtainable Key Items

Name Effect Location
Bonsly Photo Displays a Photo of 4th Gen Pokémon, Bonsly Prize for clearing Bonsly Battle Bingo Sheet
Bonsly Sheet Activate at Batte de Bingo Corner at Realgam Tower Gift for rescuing Bonsly
Cologne Case Helps Purify Pokémon Received from Fun Old Man Dentore after beating him in Agate
Data Rom Provides List of Shadow Pokémon Pick up after beating Lovelina at Cipher’s Shadow Pokemon Lab
Decoding Machine Save Overworld Pokémon Get from Prof. Kaminko
Disc Case Stores the Battle Disks Received from lady at entrance of Phenac City
Elevator Key Used to activate elevator in Phenac Training School Pick up after beating Wazzle in Phenac Stadium
Gonzap’s Key Used to get TM30 after beating Gonzap at Snagem Hideout Received from Gonzap
ID Card Used to activate restricted elevator in Cipher’s Shadow Pokemon Lab Pick up from researchers’ table there
Krane Memo 1 Memo on the Snag System Received from Joshua
Krane Memo 2 Memo on the Aurora Searcher Received from Joshua
Krane Memo 3 Memo on the Snag Machine Received from Joshua
Krane Memo 4 Memo on Purification Received from Joshua
Krane Memo 5 Memo on the Purification Chamber Received from Joshua
Machine Parts Give to Lily Obtained from machinery store in Gateon Port
Mayor’s Letter Deliver to Justy Pick up in Phenac Mayor’s bedroom
Miror B Radar Used to detect Miror B’s location Pick up at Cave Pokespot after beating Miror B
Music Software Give to Phenac Mayor Secretary impersonator Pick up at house in Phenac
Unlock Bar Used to shut down Shadow Pokemon Factory Pick up on researcher’s table there
Voice Capsule 1 Heal Overworld Combusken in Agate Village Get from Prof. Kaminko
Voice Capsule 2 Heal Overworld Poochyena in Agate Village Get from Prof. Kaminko
Voice Capsule 3 Heal Overworld Taillow in Agate Village Get from Prof. Kaminko
Voice Capsule 4 Heal Overworld Wobbuffet in Agate Village Get from Prof. Kaminko
Voice Capsule 5 Heal Overworld Shroomish in Agate Village Get from Prof. Kaminko

 
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