Mega Blocker- When the Pokemon holding this makes contact with another Pokemon, their Mega stone is made null until they switch out and they revert back if they're already Mega.
Invisibility Stone- The Pokemon is invisible (can't see it's name/model) until it takes damage.
Gust Bag- When the Pokemon holding this comes out, all hazards are cleared on both sides.
Sap Siphon- All damage done to the opponent comes back as healing. Does 25% damage per turn on holder.
Choice Sash- Restricts you to one move, but raises your defense/sp defense and lets you hit all enemies with that move for neutral/SE damage (So, it can ignore immunities and resistances and tank more effectively.)
On 12/02/12 I said I wouldn't change this until something impossible happened. Now, Earthbound just got re-released in the US.