Tox-En

Tox-En is a highly poisonous Energon variant, easily identified by its sickly green color and visible fumes. It has the opposite effect as regular Energon on Transformers, causing them to feel nauseous and weakened by the slightest physical contact. Prolonged exposure to Tox-En can outright paralyze a Transformer, eventually extinguishing their spark.

Needless to say, it's pretty nasty stuff which sane individuals will dispose of on sight. In the hands of a complete lunatic, however, it can become a devastating weapon against their enemies.

Prime cartoon
Megatron found a way to refine raw Tox-En during the war, converting it into a bioweapon that devastated the Autobots. A sample of the substance came into Autobot possession and was stored in the Vaults of Iacon. At some point, it ended up on Earth, near a volcano at the equator. It fell into an active lava flow, which carried it some distance away from its projected coordinates, but neither the container nor its contents were damaged.

During the race to find the Iacon relics, the Tox-En was found by Bulkhead. Deeming it too dangerous to leave intact, he sought to destroy it in the fiery depths of the volcano. To stall Megatron's own search party—Hardshell and a group of Insecticons—Bulkhead left a small chunk of Tox-En in the canister, along with a grenade that destroyed the chunk and left one Insecticon with a neck full of toxic shrapnel.

After leaving a false trail of Energon to keep the Decepticons busy, Bulkhead took the remainder of the Tox-En with him on his trek to the top of the volcano. Unfortunately, his earlier ruse forced him to actively carry the toxic substance, rapidly weakening his body and mind as he struggled up the slope. Although the encouragement of Agent Fowler gave Bulkhead the strength to reach the crater, his fatigue allowed Hardshell and his remaining minions to catch up to him before he could destroy the Tox-En.

During the ensuing confrontation, Bulkhead used the Tox-En as a makeshift weapon against his foes, completely incapacitating one Insecticon and sapping Hardshell's strength. After a brief battle between the exhausted Cybertronians, Bulkhead further weakened Hardshell by forcing his face into the Tox-En. As Hardshell staggered back, Bulkhead tossed the Tox-En to him, causing the disoriented Insecticon to fall into the volcano. Although Hardshell survived, the Tox-En was dissolved in the molten rock.

Unfortunately, the Tox-En exposure had taken its toll on Bulkhead; combined with a shot in the back from Hardshell, it was enough to leave him clinging to life. Ratchet was forced to put Bulkhead in stasis and diagnose him with sub-micronic system-wide shutdowns, preventing him from even beginning to operate on Bulkhead's other injuries until his patient had regained some strength. Meanwhile, Megatron was highly displeased at Hardshell's failure to secure the Tox-En, but the Insecticon managed to soothe his leader's wrath by his willingness to take responsibility for his own failure, as well as his claims of taking Bulkhead offline. Later, when Wheeljack fought Hardshell, he mockingly asked if the Insecticon couldn't handle an opponent who hadn't been weakened by Tox-En, but Hardshell replied that mid-battle banter was a sign of weakness.

Shell Game continuity
Following the death of Megatron in Viron 704.31 Epsilon, Scourge challenged Megazarak for leadership of the Decepticon and Predacon forces. Megazarak apparently backed down, only to use Tox-En to poison Scourge. He then recycled the body, using it to create the loyal but imbecilic Toxitron.

Foreign names

 * Japanese: Doku Energon (毒エネルゴン Doku Enerugon, "Toxic Energon"), Doku Ene (毒エネ) for short