What item gives the highest stat boost?

Question

Like the Choice Scarf gives a 1.5 boost to speed. What gives the highest?

Answer 1

Weakness Policy.

It doubles attack and special attack when hit by a super-effective move.

Other Stat Items for Specific Pokemon:

Deep Sea Scale - Doubles Clamperl's Special Defense
Deep Sea Tooth - Doubles Clamperl's Special Attack
Light Ball - Doubles Pikachu's Special Attack and Attack
Quick Powder - Doubles an untransformed Ditto's speed.
Thick Club - Doubles Cubone's and Marowak's Attack.

Source: Experience & this (thanks, LolAlex =3)

Comments

You should add the following items in the list: Deep Sea Scale/Tooth, Light Ball, Quick Powder, and the Thick Club. Even though these are pokemon specific items, each one doubles a specific stat! http://bulbapedia.bulbagarden.net/wiki/Stat-enhancing_item