Firebat/1.03.24

Firebat is a basic flier. Firebats can be misleadingly good in certain conditions. Although their combat is poor and their damage output is pretty low, their fire type attack, however, allows them to chew through buildings with surprisingly good effectiveness. But with poor HP and pathetic armor, they are usually killed outright by any attack. As such, you'll need a respectable sized swarm for them to survive against typically placed towers long enough to be threatening and ideally you'll want them to pretty much kamikaze into the enemy base - ignoring the towers completely and target high value buildings, such as keeps and Eyries / Nests / Broods - burning them down to rubble before going up in smoke themselves. Of course, they fare even better against towers that use elemental attacks - hitting their higher resistance and even allowing them to survive an attack or two. Although they possess a resistance to fire type attacks, they can be upgraded further in this regard. This makes them all but unstoppable at tearing down fire attack based buildings, such as those seen from Daemons, Dark Elves (with no ranged units garrisoned), Swarm and Ssrathi (with ranged units garrisoned).

Dark Dwarves
Although Dark Dwarves have plenty of answers for buildings, Firebats further their already broad options to include aerial assaults. However, due to their natural frailty, they're best used as opportunists and hit your opponent's buildings when they're least defended. Typically you would want to keep them back and swoop in to the enemy's base from the opposite side to target highly valuable buildings (Keeps Eyries / Nests / Broods) once you've lured the enemy units out with your siege weapons banging at their front door.

Benefits from Armorer and Mithril researches.

Daemons
Firebats are one of the best basic fliers around. Unfortunate for them, one of the two races that produce them, in this case Daemons, have access to a variety of flying units that tends to make it difficult for Firebats to stand out. Imps are their main rival for the spot light who are not only available earlier, but also more disruptive overall and can be summoned for free. But it's not all doom for the infernal Bat, for their ability to shrug off fire type attacks like they were nothing allows Firebats to "wall" enemy towers that deal fire typed damage. Although this itself is a pretty minuscule trait due to the lack of fire damage towers, but there are those few occasions where you may need to something to sponge fire attacks and be expendable at the same time to scout for hidden attack types lurking in other towers, that would otherwise catch you off guard and prove fatal for something much more valuable.

The Doombat research is specifically for the Firebat and also benefits from the Daemonic Sight research.