Changes form/boosts move power
Red Orb
Blue Orb
Shock Drive
Burn Drive
Chill Drive
Douse Drive
Adamant Orb
Adamant Crystal
Lustrous Orb
Lustrous Globe
Griseous Orb
Griseous Core
Rusted Sword
Rusted Shield
Plates
Blank Plate
Legend Plate
Memories
Bug Memory
Dark Memory
Dragon Memory
Electric Memory
Fairy Memory
Fighting Memory
Fire Memory
Flying Memory
Ghost Memory
Grass Memory
Ground Memory
Ice Memory
Poison Memory
Psychic Memory
Rock Memory
Steel Memory
Water Memory
Stat-enhancing items
Leek
Light Ball
Lucky Punch
Metal Powder
Quick Powder
Thick Club
Z-Crystals
Aloraichium Z
Decidium Z
Eevium Z
Incinium Z
Kommonium Z
Lycanium Z
Marshadium Z
Mewnium Z
Mimikium Z
Pikanium Z
Pikashunium Z
Primarium Z
Snorlium Z
Ultranecrozium Z
While almost any Pokemon can technically hold these items, thus negating their exclusivity, the effects can only be utilized by a select few Pokémon. This is why items like most of the Plates are not on this list, as while only Arceus can use them to change forms, other Pokémon gain a boost to their moves. This does not apply to the Blank and Legend Plates.
Held items (Bulbapedia)
Hope I helped! If I missed anything, let me know.
