A reality bomb is a doomsday weapon of Dalek origin.
In addition to the advanced technology required, a reality bomb requires 27 planets with particular characteristics arranged in a precise formation. When the entire system is in place, the reality bomb can cause arbitrary quantities of matter to disintegrate completely. At maximum potential, the reality bomb can destroy all matter in the universe and in all parallel universes, making it the ultimate weapon of mass destruction.
The most obvious limitation on the weapon is finding planets with the necessary attributes and then relocating them so that they form a system with the correct configuration.