An Energon-draining variant of Terrorcon was created when Starscream and Knock Out mixed Synthetic Energon with Dark Energon. Due to the imperfect Synthetic Energon formula causing Transformers to run through their natural Energon reserves abnormally quickly, these Terrorcons developed a thirst for Energon that prompted them to attack other Transformers in order to drain their Energon. They also developed a bizarre proboscis in their mouths for draining Energon. The Dark/Synth-En Terrorcon mutagen could be passed on to other Transformers by a single bite, and it could turn both living and dead Transformers who were bitten. Unlike the Terrorcons created with Dark Energon alone, the Dark/Synth-En Terrorcons were completely immune to Megatron's mental control, theorized by Knock Out to be due to the mutagen's Synth-En component corrupting Megatron's link to the Dark Energon component.
Unicron, as the source of Dark Energon, was capable of manifesting it at will in order to create Terrorcons. He was able to use it to revitalize Megatron and possess him, and later raised an army of fossilized Predacons to serve him. When Unicron was defeated, his army exploded into dust.
Main Article: Terrorcon Gallery
- Cliffjumper (deceased)
- Skyquake (currently in Shadowzone, possibly destroyed by Soundwave when he is trapped in the Shadowzone too)
- Various Unnamed Terrorcons (deceased)
- Terrorcon King - featured in Transformers: Universe
- Breakdown/Silas (deceased)
- Airachnid (on Cybertron's moons, status unknown)
- Many Insecticons (on Cybertron's moons, status unknown)
- Vehicons (deceased)
- Predacons (deceased)
- The term Terrorcon was first used in "Loose Cannons" when Arcee was describing Skyquake's zombie revival, which was caused by Starscream.
- Terrorcons seem to be limited in their fighting abilities as none of them were ever seen transforming, using their built in weapons or even able to speak, the exception being the Dark/Synth-En Terrorcons.
- Many fans believed that Dreadwing and Makeshift would become Terrorcons in Thirst.