Although the title seems counterintuitive this is perhaps the most usefull of the Power-Ups Line. Often when translating an ability from fiction or defining something you came up with on your own making it unique is as much what you take away from the stock advantages as what you add. This book compiles and expands on the existing limitations in GURPS in marvelous ways alowing far more customization of abilities. If you use Gurps it's well worth buying.