The Inferno Tower doesn't have a favorite target, nor does it deal more damage to any troop more than the others.
The Inferno Tower in single-target mode is weak against large numbers of Tier 1 (and to a lesser extent Tier 2) troops. Make sure the Inferno Tower is within range of a Mortar or a Wizard Tower so that it is adequately defended.
This defense, when set in single target mode, is tailor-made to destroy the most powerful of troops, such as the Dragon, P.E.K.K.A and Golem. As such it is a perfect complement to a Wizard Tower, which is very effective against large numbers of weaker troops but struggles against those with high health pools. Positioning these two structures close by can substantially improve the survivability of both structures (and the rest of your base).
The tower's heating effect restricts the healing of its targets, so it is best to place them near the most important buildings like storages or the Town Hall.
This structure (especially in single-target mode) wreaks havoc with most common offensive strategies where heavy units go in first to distract defenses and light units follow. Letting your heavy troops get in range of it spells certain doom for them, even high-level Heroes. A combination of Lightning Spells and a group of Minions may be the best way to get at the Inferno Tower if it is behind multiple Walls and defenses.
Small troops are stronger against the Inferno Tower in single-target mode, as every time it targets a new troop it will have to heat up again. Golems get destroyed in seconds by this strong defensive building, but if you surround it with Archers or Barbarians it will be defeated very quickly. In single-target mode it can only target one unit at a time, so attacker spacing is not an issue (unless a Wizard Tower or Mortar is nearby).
You can tell if an Inferno Tower is in single or multiple target mode by looking at its top. If it has one large hole, it's in single target mode; if it has three small holes, it's in multiple target mode.
Look at the Inferno Tower to see if it is empty or full with Dark Elixir. If it is empty there will be no canister of Dark Elixir attached to the side of the tower, and there will no longer be fire emitting from the top. Also the glowing lava pool present at the bottom will have also disappeared, giving the entire structure the look of ordinary rock or metal (see image gallery below).
Inferno Towers do not undergo any significant visual changes.
When initially constructed, the Inferno Tower consists of a tall, narrow tower of rocks straddling a glowing pool of lava. At the top of the Inferno Tower is a circular focusing lens, and a rectangular-shaped Dark Elixir reservoir is mounted on one side.
At level 2, huge red flames are emitted from the focusing lens on the top of the tower, and the prominent sections of rock from the first level become gilded with a red overlay. The rock holding the lens becomes gold and the lens themselves become red and the fire overwhelms the ring.
At level 3, its structural supports become thicker and gain spikes. Also, the structure that contains the fire becomes a hollow faceted frame.
It was Added on the May 23, 2013 update as part of the 'Fiery Fortress' Update.
It is currently the last defense unlocked.
It takes up a 2x2 space. This means Inferno Tower, along with the Hidden Tesla, occupy the smallest space in the village of any permanent defensive structure.
There are currently only 2 upgrades available, giving the Tower a total of 3 levels. This gives it the least amount of upgrades of any building (aside from the Builder's Hut, which has no upgrades at all).
It is similar to the X-Bow due to the fact that both have limited ammunition, must be periodically reloaded and have two modes.
Although the Inferno Tower is reloaded with Dark Elixir, it shoots out a continuous line of fire.