The Inferno Dragon is a flying Baby Dragon that attacks with an inferno beam that builds up damage over time, much like the single-target Inferno Tower.
Boosting the Baby Dragon requires 25,000 Dark Elixir or a Super Potion, and doing so allows the Baby Dragon to be boosted for 3 days. The level of Inferno Dragon you obtain from the boost corresponds to the level of Baby Dragon you have.
Because of the level requirement, players require Town Hall 12 in order to be able to boost Baby Dragons into Inferno Dragons. However, Inferno Dragons can be donated to any level 2+ Clan Castle, allowing most players in a clan to use one.
Inferno Dragons have no preferred target when attacking; they will simply attack the closest building. However, once they become aware of enemy Clan Castletroops, Heroes, or Skeleton Trap skeletons (either by being attacked themselves or by being near another friendly troop under attack), they will leave their previously targeted building and instead engage the enemy troops. Once all of the nearby enemy troops are defeated, the Inferno Dragons will proceed to attack the nearest structure.
Offensive Strategy
Inferno Dragons can serve very well as part of air attacks, as they have the capability of taking down high health buildings quickly. They also have no loss of DPS when next to other troops as well.
This is especially good for LavaLoon attacks, where you can send them with the main army and let them take down the defending Queen and Champion, allowing other troops to be used elsewhere (E.G. allowing a Queen Charge to target something else like Town Hall.)
The Air Sweeper should be a defense to watch out for when using Inferno Dragons. The sweeper's pushback will send the Inferno Dragon out of range of its target, resetting its damage.
Inferno Dragons can be quite poor at taking out moving targets, particularly a defending Barbarian King, as they will often need to retarget whenever these targets move. However, against defending Archer Queens and Royal Champions, multiple Inferno Dragons can easily defeat them because the defending heroes will usually stay in place.
Like their non-super counterpart, they can be used to create funnels as well, but this is only better than a Baby Dragon when there are lots of high HP buildings, due to it's less space-efficient health and lower low-level DPS.
Against a defending inferno, bring a lightning spell. It resets the charge and deals a good amount of damage, along with one-shotting other commonly used clan castle troops.
Against a defending Inferno Dragon, you can swarm it with troops that have low housing space, or you can use your archer queen if she is high leveled (at least level 45)
Defensive Strategy
Inferno Dragons are superb Clan Castle troops. Their ramping damage acts as movable inferno towers on defense. A Freeze Spell/Poison Spell is almost always required to save the tanks and Heroes from this troop.
Inferno Dragons are slowed down by low HP buildings. Putting them around your heroes can buy time before they are targeted by the Inferno Dragon.
Also put them around high damage buildings, so they can kill or do major damage to the dragon before they get destroyed.
An Air Sweeper is detrimental to the Inferno Dragon. Protect them well and make them cover the whole base to destroy Inferno Dragons.
Inferno dragons are far less health efficient than their counterpart. Focus on making high damage areas to waste their space taken.
Trivia
You can have a maximum of 20 Inferno Dragons at one time in a complete set of fully upgraded Army Camps. This number increases to 23 if you include the 3 that can fit into a fully upgraded Clan Castle. On the battlefield, you can clone an additional 6 Inferno Dragons with three level 5 or higher Clone Spells.
The Inferno Dragon is the only one of nine Super Troops to have been transferred from Clash Royale.
The Inferno Dragon's artwork is shared with Clash Royale. Despite coming after the one in Clash Royale, the artwork was originally made for Clash of Clans.
The Inferno Dragon was added to Clash Royale on 30/9/2016. The descriptions in Clash Of Clans and Clash Royale both mention how the Inferno Dragon's beam deals higher damage per second over time. The Inferno Dragon was added to Clash of Clans in the 2020 Summer update along with Super Witch.
It is said that the Inferno Dragon has learnt to focus its rage into a very powerful beam (its inferno attack), possibly revealing why the Inferno Dragon no longer goes into a raged state when alone.
The Inferno Dragon was first revealed in a dark silhouette at the end of a developer livestream. That was the only thing known on its "confirmation".