Tasmanian Devils were once thought to have been one of the few species on Mobius that never fully evolved after the Xorda Attack on Earth as they didn't seem to share the same intelligence as most Mobians. This later proved false, as they once had the most advanced culture in Downunda and were mutated by the Echidnas. The vast majority of the race has been transformed into savage animals, commonly known as Devil Dogs.
During ancient times, a rogue group of Echidnas from Albion arrived in Downunda and used genetic engineering to transform a tribe of Tasmanian Devil Mobians into less intelligent vicious dogs, which they used as beasts of burden and for guards. The Echidnas were subsequently punished for their crimes, but the damage had been done, and the race ever after recited the story of the Echidnas' crimes to their children. The so-called "Devil Dog" version of the species became more and more prevalent as the generations passed, whilst the former Mobian version all but disappeared. Thrash is one of the only known examples of a sentient Tasmanian Devil left on Mobius, and most outsiders believe that the Devil Dogs are the natural form of the species. Ruins of the Tasmanian society remained in Downunda as a testament to the failing race.
Their keen sense of smell makes them good for tracking scents, so they were used by Geoffrey St. John, Smiley, and Fleming to help find the prisoner Sonic the Hedgehog after he escaped from a crashed plane headed for the Devil's Gulag. Whatever his feelings regarding his people's use in such ways, Thrash would serve the Kingdom of Acorn in his own way by briefly teaming up with the Downunda Freedom Fighters and the Chaotix against the Downunda Dark Egg Legion.
Accompanied by a pack of Devil Dogs - including his two "sisters", who were Devil Dogs born in the same litter - Thrash set out on a quest to find and punish the Echidna society for mutating his people. His quest eventually led to the banishment of all but a handful of Echidnas to parts unknown through a Warp Ring. As a result, however, Thrash and his pack became embroiled in battle with Knuckles the Echidna and Team Fighters in the Echidna homeland of Albion. After a fierce conflict, Thrash's pack was trapped in an enclosure by Team Fighters, who later released them so they could help fight the Krudzu Hybrid Hydra, while Thrash himself escaped, but was pursued by Knuckles. Thrash considered his actions just, and felt that being left the last surviving members of their Mobian races made him and Knuckles equal. Their battle led them across Mobius, including to one of the Tasmanians' ruined settlements. Here the pair encountered another surviving (albeit ancient) Mobian Devil and a pair of Devil Dogs, before pursuing their battle to White Acropolis and then to Angel Island, at which point Thrash made his final escape.
Their keen sense of smell makes them good for tracking scents, so they were used to help find the prisoner Sonic the Hedgehog after he escaped from a crashed plane headed for the Devil's Gulag. (StH: #48)
- Thrash seems to be a fully evolved Tasmanian Devil, but Doctor Finitevus refers to him as the "remainder of a failed experiment".
- Tasmanian Devils are natural predators to Echidnas, hence why Thrash has hatred towards all Echidna kind.