This paper studies to which extent the social welfare of a game can be influenced by an interested third party within economic reason, i.e., by taking the implementation cost into account. Besides considering classic, benevolent mechanism designers, we also analyze malicious mechanism designers. For instance, this paper shows that a malicious mechanism designer can often corrupt games and worsen the players’ situation to a larger extent than the amount of money invested. Surprisingly, no money is needed at all in some cases. We provide algorithms for finding the so-called leverage in games and show that for optimistic mechanism designers, computing the leverage or approximations thereof is NP-hard

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