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There are all sorts of accessories available in the game, and each bestows a different combat advantage. You'll want to get a hold of a wide selection so you can pick and choose between battle strategies.

Name	Description	Where to find/purchase
Power Wrist	"Strength" +10
Protect Vest	"Vitality" +10	Receive after defeating Rufus in Shinra Bldg
Star Pendant	Protects against [Poison]	Receive for trading in A Coupon on the 63rd floor of the Shinra Bldg; Receive for defeating Motor Ball boss
Talisman	"Spirit" +10	Receive after defeating Sample: HO512 on the 67th floor of the Shinra Bldg
Touph Ring	"Vitality"&"Spirit" +50