Dark Star Saber

The Dark Star Saber is a sword made from pure Dark Energon. Intended to be a dark counterpart of the Star Saber itself, this blade possesses all the powers of the original blade, and is even stronger than its counterpart. Unlike the original blade, the Dark Star Saber doesn't require a Prime to activate its powers. It also appears somewhat sentient as it can resist certain individuals but even they can still use the blade's powers to an extent.

Prime cartoon
Megatron, after securing the arm of a dead Prime, used the Forge of Solus Prime to craft a counterpart to the Star Saber out of a huge chunk of Dark Energon. Megatron first brought the blade into action after the decoding of the next Iacon relic in Egypt, and used it to make fools out of Arcee and Smokescreen. The waves of energy it created threw Smokescreen against a pyramid. When Optimus arrived with his own Star Saber, the two engaged in battle, but the Dark Star Saber would prove to be stronger, breaking Optimus's sword.

Megatron took the sword with him to Cybertron to find the Omega Lock. He got the opportunity to use it when the Autobots showed up, and Optimus attacked him with the reforged Star Saber. Megatron was confident that he could destroy the blade a second time but the Autobots escaped with the Omega Keys before he could do so. It also proved capable of destroying the Spark Extractor when Smokescreen used the device against Megatron's men. After Megatron began using the Omega Lock to cyberform Earth, Optimus charged at him with the Star Saber. Megatron managed to counter his first blow using the Dark Star Saber, only for Optimus to slice his sword arm off at the elbow. Both sword and arm were subsequently caught in the explosion when Optimus destroyed the Omega Lock.

Knock Out and a squad of Vehicons headed back to Cybertron to retrieve any relics they could, the Dark Star Saber being one of those which were found and stored it in the Nemesis vault. When Predaking turned on the Decepticons for Megatron terminating his Predacons, Megatron decided to test the sword against him. Predaking found him before he could reach the vault, however, and Megatron was forced to outwit him without its might. Knock Out brought the sword moments too late for it to be of use against Predaking, but just in time to be used against an imminent Autobot attack on the ship.

He got the chance to employ it against Optimus when the Autobot leader attacked the warship. As the Autobot leader flew towards the ship, Megatron used the blade to take out the Autobot's jetpack. Optimus did eventually get to the Omega Lock, only for Megatron to attack him yet again with the blade, but this time Optimus managed to knock it out of his hand. After Megatron terminated Bumblebee, the Decepticon leader used the dark blade to knock Optimus off the ship and cling for his life. Before Megatron could finish the job, he was killed when Bumblebee, who had been resurrected by the Omega Lock's energies, ran him through with the original Star Saber. As Megatron died he tried to run him down with the Dark Star Saber, only for it to fall from his grip and plummeted towards Earth.

2015 Robots in Disguise cartoon
The Dark Star Saber was found at the bottom of the Earth's ocean by Clawtrap and the Scavengers. However Starscream showed up, tracking down the Minicons, and quickly reclaimed the sword. Strangely, the Dark Star Saber was starting to reject him. He observed that the sword seemed to think he wasn't totally worthy of it, but continued to utilise it anyway, including threatening Bumblebee and hunting "Earth rodents" when not carrying it clamped to his back at all times aboard his ship.

When Starscream went into battle against the Autobots and Weaponizer Mini-Cons, the Dark Star Saber showed the ability to unleash a pulse of stunning electricity, knocking out the Seeker's opponents to the last bot. Following his defeat by Optimus Prime, the Dark Star Saber was locked away on Optimus' ship for safe transport back to Cybertron.

Transformers: Devastation
Optimus Prime's Nemesis Prime DLC skin comes bundled with the Dark Star Saber instead of Optimus's default energon-axe.