context: Richard B. Riddick has been in hiding for five years, evading bounty hunters and mercenaries sent to capture him. After killing a crew led by Toombs and stealing his ship he heads to New Mecca in the Helion System, after Toombs reveals his bounty originated there. Riddick is reunited with Imam, the man previously rescued. Imam believes Riddick is a Furyan, a race of warriors long thought extinct, and wants to know about his homeworld and if anyone other than himself is left. Imam believes Helion Prime is the next planet to be conquered by a mysterious force crusading across the stars. Aereon, an Air Elemental, identifies the army as the Necromongers, religious fanatics who seek to convert everyone and kill those who refuse. The Necromongers attack, and take control of the capital in a single night. In the battle, Imam is killed and Riddick escapes.
  The next day, the Necromonger high priest called 'The Purifier' coerces the populace into converting, except for Riddick, who kills the man who killed Imam. Intrigued, the Lord Marshal orders Riddick be scanned by the Quasi-Dead, half-dead telepaths, who determine that he is indeed a Furyan survivor. Lord Marshal orders Riddick's death, but Riddick escapes only to recaptured by Toombs. Riddick is taken to Crematoria, a harsh subterranean prison moon, where Jack, a girl Riddick rescued, is also held.
  The Lord Marshal sends Commander Vaako to hunt Riddick down. Vaako's wife speaks to Aereon, who reveals that Furya was devastated by the Lord Marshal after he was told a child from that planet would kill him. Dame Vaako and her husband determine Lord Marshal wants Riddick dead, as he may be the child of said prophecy. On Crematoria, a disagreement breaks out between Toombs and the prison warden over what Toombs is owed for Riddick's bounty. Word about the Necromongers has reached the prison warden, who deduces that Toombs has stolen a prisoner from the Necromongers. Meanwhile, in the prison, Riddick finds Jack, now named Kyra, and they eventually reconcile.
  The guards kill the bounty hunters, take the reward money and prepare to leave before the Necromongers arrive. Riddick leads several prisoners across Crematoria's volcanic surface to steal the ship. The guards reach the hangar, just as the prisoners arrive to find the Necromongers have cornered them there. All of the guards are killed and Riddick is incapacitated by Vaako. With the approach of the vicious sunrise (from -300 to 700 degrees in seconds), Vaako leaves Riddick to die; Kyra is captured by the Necromongers.
  However, Riddick is saved by the Purifier, who tells him that if he stays away from the Necromongers, the Lord Marshal promises not to hunt him. The Purifier then reveals that he too is a Furyan before committing suicide by walking out into the scorching heat after encouraging Riddick to kill the Lord Marshal. Meanwhile, Vaako reports Riddick dead and is named heir apparent by the Lord Marshal. Riddick flies back to Helion Prime using Toombs' spacecraft.
  Riddick, infiltrates the main hall; Dame Vaako sees him, but encourages her husband not to warn the Lord Marshal, but to let Riddick strike first and pave the way for Vaako to kill the Lord Marshal and take his place as leader. When Riddick attacks, the Lord Marshal presents Kyra, who appears to have been converted. Riddick fights the Lord Marshal one-on-one in front of his army, who prevails with his unnatural powers. When it appears that Riddick is about to be killed, Kyra stabs the Lord Marshal in the back with a spear. The Lord Marshal punches her into a column of spikes, mortally wounding her. Vaako then makes his move to strike the wounded Lord Marshal, but misses. Vaako's attack allows Riddick the opportunity to deliver a killing blow. The film ends with Kyra dying in Riddick's arms just before the Necromongers, including Vaako, kneel before Riddick as their new leader.
question: What weapon did Riddick use to kill Lord Marshal?
answer: Unnatural powers