Weaponless Elite glitch
From Halopedia, the Halo wiki
To exploit the Weaponless Elite glitch, you must go to the level, Metropolis in Halo 2 and board the Scarab. Throw a Plasma grenade at the Scarab operator while is operating the Scarab. He will will make the animation for a Energy sword but won't have one. Easy is the best difficulty for this.