There is a list of items that are immune to any form of in-battle manipulation:
- All Mail items (in games where they exist, except Japanese Ruby/Sapphire)
- All Z-crystal items
- Griseous Orb, but only if it's held by (or a move's effect would attempt to give it to) Giratina
- All Plate items, only for Arceus
- All Drive items, only for Genesect
- All Mega Stone items, only for the correct user of the stone
- Red Orb, only for Groudon (in Sw/Sh the Red Orb doesn't exist, and when checking for Groudon's "signature item", what it actually checks for is that it's not holding an item)
- Blue Orb, only for Kyogre (same disclaimer as above)
- All Memory items, only for Silvally
- Rusted Sword, only for Zacian
- Rusted Shield, only for Zamazenta
If an item meets this signature item check, then Trick and Switcheroo will fail when used by either side; Fling and Bestow fail when used by the holder; Thief, Covet, and Knock Off can still be used by the opponent to deal damage, but won't remove the item; and Pickpocket, Magician, and Symbiosis won't trigger if that trigger would involve the transfer of an item that's considered signature to either side. As most of these are form-changing items, this prevents any possibility that the Pokemon could be forced into an unwelcome form change in the middle of battle.
