The following section contains information from a previous version of StarCraft II which is no longer valid.
The hellion went through 600 design changes over the course of development. Various names were pitched, including the jackal, loki and fire bike. In its earliest stages, the vehicle was a hoverbike much like the Vulture, and possessed a powerful anti-infantry railgun. Eventually the design settled upon was a three-wheeled vehicle. The response on the development team was rather mixed about the three wheeled version, and while taking an opportunity to quickly make non-lethal civilian variations the four wheeled version was made. The three wheeled version was reused for the Outback Hunter.
The hellion had a total of eight upgrades named Napalm Fuel Tanks, Thermite Filaments, Turbo-Charged Engines, Twin-Linked Flame Thrower, White Napalm, Viral Plasma and two versions of Infernal Pre-Igniter. Only Twin-Linked Flame Thrower and Thermite Filaments are used in the release version of the Wings of Liberty campaign, with Infernal Pre-Igniter being the only upgrade in multiplayer.
Turbo-Charged Engines greatly increases the movement speed of the Hellion, with Viral Plasma and White Napalm increasing the base damage of the hellion's weapon. The old version of Infernal Pre-Igniter decreased the delay between shots by 0.75 seconds instead of granting bonus damage. Napalm Fuel Tanks however has no effect in-game as it remains incomplete.
Heart of the SwarmEdit
As of January 2013, the hellbat no longer gains a damage upgrade from the pre-igniter upgrade.