A Fire Drake is an upgraded Firebat, with increased speed, range, and firepower.
During the Second Great War, it became apparent that Firebats, while good at close quarters, were not effective at range. A number of Firebats began to add to their suits, removing heavy armor plating in favor of lighter armor plating. Scavenged Reaper jetpacks were strapped to their backs, forming a Reaper-Firebat combo. Finally, a new flamethrower design was installed, increasing the effective range dramatically. These newly dubbed, "Fire Drakes," allowed for higher mobility and longer range, making them useful in wide open battlefields. Sadly, the Zerg forces retreated before they could see widespread use, however the newly reformed Dominion took interest in the designs.
Fire Drakes move much faster than regular Firebats, but have less hit points. They automatically switch between Flamethrowers and Firelaunchers depending on the range of their target. If a target comes in range of the Flamethrower, while the Firelauncher is targeting another unit, the Fire Drake will switch to it's Flamethrowers.
Flamethrowers are most useful when multiple enemies are melee attacking the Fire Drake, as it has a wide spread but not that much damage. The Firelauncher on the other hand targets one unit from a distance, dealing heavy damage with a medium cool down. Both attacks have a chance of applying a Burning debuff, which for a short while will cause the unit to lose health.
The jet-pack worn by the Fire Drake increases the speed of them, but also by activating Thruster Boost the Fire Drake can jump approximatly two cliffs, up or down. This can be used to allow the Fire Drake to jump up a cliff, engage enemies, then jump back down. There is no time limit between the two jumps, but the ability will only start to cool down once both jumps are used.