This will be a question that I am fine with having less realism in. I was thinking of a weapon, like a spear, that can go at FTL (faster than light) speeds. To be clear, the spear is FTL due to propulsion (that is where the realism fades) rather than being a miniature Alcubierre Warp Drive (that creates a space-time bubble that eats matter around it), so when the spear hits someone, they are still being hit by a solid object (that is, if the spear does not get destroyed immediately).
The thing is, I have little idea of the ramifications of being hit by something going FTL. I know that an object that is moving at speeds nearing that of the speed of light can already have enough power to create earthquakes and rival nuclear weapons in terms of devastation. But what about beyond the speed of light? Can kinetic energy even be used anymore for such a weapon?
EDIT: Since you want to know how the FTL was supposed to work, I was thinking of using concentrated Dark Energy as a propellant, expanding space behind the spear to make it look FTL.