"If it rampages, it knocks down mountains and buries rivers. Maps must be redrawn afterward." (Diamond/Pearl) Tyranitar.
I found this one on the gamesradar site. They talk about how it's destruction of mountains would be bad for the population of their own species as Larvatar needs to eat a mountain to evolve, but I find the fact that maps are constantly being redrawn due to this thing waking up on the wrong side of the bed to be hilarious as the map business would be amazing and the games never seem to have a problem with these sudden change in landscape. Maybe Tyranitar hibernate as most games come out in the fall.
Also, why do terrorist organizations not use these things
It seems like a better strategy to anger a few of these and lure them to the city.
But then again, there may be a ten year old kid, and they are enough of a threat without a giant monster of a pokemon under their command