Overly-Great Thing

You can have this magical orb that grants your every wish, but it comes at a price: any wish you make will be granted, but it'll have an odd quirk thrown in.

The thing that has a power that makes it overpowered to our heroes but might have a trait that counters this power, something like what the slidetext said (having the usage of this power come at a price) or never being able to be used because of how the Overly-Great Thing is always moved just as the heroes use it. This normally is found on 2Gud4U.net as the heroes may never even get a chance to use the elusive Overly-Great Thing and are chasing it around. This may sometimes be the premise of the franchise they're in. The closest they may get is being Mere Moments Away from using it, but a Hex Machina, like a giant bird, might take it away.

Examples of Overly-Great Things
Samurai Jack - VII. The episode surrounds Jack's attempt to get to the top of a tower for a wishing well that is guarded by three archers. In the end, Jack makes it to the tower top, frees the archers who were under a spell of Aku's, and destroys the well after he hears that something like what the slidetext said would happen to whoever makes a wish to the well.