Minoru, Pragmatic Dealer

Whenever an artifact enters the battlefield
under your control, players may pay X amount
of life, where X is any number of their choice.
The opponent that pays the highest amount of
life gains control of that artifact. At the beginning
of the next end step, that artifact is exiled.
Being inventive is far more useful than being
ambitious. Both would be cool, too, but you get
the idea.