The Remnant-Changeling queens that have been disavowed by their Empresses, griffin nobles that have been convicted of treason against the Moot, minotaurs cast out of the Senate and Minotaur Republic, ponies that go Evil Overlord, and shunned zebras can become this.  They’re very dangerous because they have nothing to lose, quite a bit of resources, and will do something with the resources they have.  Especially in the case of changeling queens and griffin nobles, they have ships and resources and will try to create their own nation (or at least pirate kingdom).  They’re especially dangerous than the average run-of-the-mill pirate because they have access to (relatively) current military technology and usually have discipline.

This is the big reason why the major powers send out task forces or whole fleets whenever punitive missions against pirates must be done.  It’s also the reason for the existence of the Princess Luna-class fast battleship (and it’s Imperial Griffin Navy equivalent.)