Dragon

Dragon is a fearsome nit of clash of clans. Unlike balloons they have range and can deal splash damages like wizards. The splash is short ranged and only effective against clan castle troops. Dragon has a huge health and much effective to defend your village.
Dragons have green colour skin and black eyes in level 1, when they are unlocked in barrack first. After upgrading them in the laboratory they become purple colour like the picture in the barrack. Their eyes also become the colour of elixirs in level 2. At level 3 they get greyish brown skin colour. Dragon's skin become deep red and it's known as ancient red dragon. Their eyes also start to flame. At level 5 they get golden horns near their head and golden spikes on their back. Their wings become larger. Level 5 is currently the maximum level of dragons.

Dragon is one of the strongest as well as effective units of clash of clans. Dragon have a huge hitpoint which helps him to take a lot of damages from defensive buildings even from air defence tower. When dragon is used to defend your village it is difficult to kill him because of his huge health. Its hitpoint will also used as a shield to protect balloons from air defence’s attack. Initially it gets 1900 hitpoints. It gets even stronger after it gets upgraded in the laboratory.
The hitpoints of various level dragons are:

Dragon is a mighty warrior that attacks both ground and air units. This particular characteristic made this unit one of the best troop of clash of clans. When dragons are used as clan castle troop it can take care of any enemy unit. Same thing happens when you attack with dragons and the opponent clan castle is filled up with defensive troops. Unlike balloons they attack opposition dragon, minion, balloon etc. Moreover dragon itself is a air unit. So all ground defences like Mortar, Canon even x bows that are triggered to ground do not attack dragons.

Dragon has a huge damage per second relatively, though its very low compared to per housing cost. But As a unit dragon has comparatively higher DPS than most other troops. Upgrading them in the barrack will make them fearsome unit. Another thing is dragon’s damage is splash type. So it can deal same amount of damage to multiple units at a time. DPS of various level dragons are:

Splash damage is another good thing of dragons. Dragons have 0.3 tiles of area splash effect. They deal similar amount of damages to multiple units. Though its splash range is relatively smaller and effective only on enemy troops, sometimes it works good against melee troops. Usually dragons do not attack walls but if they attack enemy troops closer enough to walls, its splash damage effects the walls and deal damages. When first dragon was introduced as troops they didn't have splash damage. Later at the middle of 2013 supercell made their attack type as splash damage and dragon got themselves much more powerful.
Range: Dragons have a effective range of 3 tiles. You can feel the need of having range when you attack with balloons. Dragons range helps them to attack enemy troops as well as defensive buildings from distance and sometimes keeps them away from air defence tower's range. Range will give some advantage to dragons against their moderate movement speed. When dragons are used to defend your village sometimes they can attack the enemy troops being in the range of your defensive buildings because of their range.

Dragons take a huge housing cost. It takes 20 spaces in the barrack. In town hall 7 when you first unlock the dragon, you will take at most 10 dragons at a time. This huge housing cost is a weak point of dragon attack. For this reason players like to use some balloons with their dragons. Balloons require 5 supply cost for each. So you can use 4 balloons in the space of 2 dragons. Balloons target the defence first and dragon takes a lot of damages.

Dragon is undoubtedly an expensive unit. Dragon requires 25 thousand elixirs to train each when they first unlocked to barrack. That means 1250 elixirs for per housing space, which is costly than most other troops of COC. Their training cost increases every time they got themselves upgraded to next level in the laboratory. Training cost is one of the reasons that players are not interested to use dragons for farming purpose. Training cost of every level dragon is:

Dragon has a movement speed of 16. It is one of the slowest units of the entire game. It’s speed can reduce the effect of high hitpoint as it will gain more damage. Moreover sometimes you’ll find your multiple dragons to the same target which can be easily took down by one dragon. It slows down your attack and often you’ll end up in 2 stars only because of its slow speed. It’s good to take some archers if you want 100% of your opponent base.

Dragons require a huge training time. It takes 30 minutes to train each dragon, 1.5 minutes for each supply cost. Dragons training time is one of the biggest drawback of this unit. Farming bases do not use dragons because of this long training time. In higher town hall level using a lot of elixir doesn’t matter that much. But still dragons are not used in multiplayer battle because of this reason.

Dragons do not have any preferred target. They just attack any building/unit closest to them. Once they are aware of clan castle troops they target them and after defeating them target the nearest building from their current location. This is a weak point. Because dragons get a lot of damage from air defences while they are destroying other buildings. Usually anti dragon bases are used to be designed such a way that storage buildings are placed in front of air defence. Storage buildings have relatively a higher hitpoint than defences. So dragons need more time to destroy them while air defence targets and hits them continuously.
Unlike dragons, balloons have preferred target of defences. For that reason balloons are used with dragons to destroy the air defences so that dragons can survive and destroy the whole base.

Dragons require a lot to upgrade to the next level. It requires 20, 00000 elixirs to upgrade from level 1 to level 2. It’s upgrading cost gradually increases as they’re upgraded to other levels.
The upgrading cost of different level dragons is:

Most of the Dragon strategies are based on taking out as many air defence as possible because this is the biggest weakness of this unit. Dragon strategies are very much depended on spells. In town hall level 7 when you’ll be able to unlock dragon for first time you will have 3 spells. You can take 3 lightening spells to take down 1 air defence. Or you can use 2 healing spells and 1 rage spell or 1 healing spell and 2 rage spells depending on the opponent’s base. Taking 100% from a town hall level7 with Dragons is a pretty easy job even with level 1 dragons. But it becomes tough when you get yourself upgraded to town hall 8. In town hall level 8 neither you get a new spell nor a camp upgrade. So technically you’ll have to deal with a town hall level 8 with almost the same troops as town hall 7. You can upgrade your dragons to level 3 that’s the diffrence. Here dragon strategies are implemented effectively. In a town hall 8 max base you will have to fight against 3 level 6 air defences and level 10 archer towers. Both of them are really good and can shot down your dragons easily. Light spell/ Rage-heal spell strategies are simple. You will use 3 lightening spells to destroy a air defence when the air defences are far from each other or you can destroy other two air defences with your troops (Giants/balloons). And the Rage-heal attack are implemented when the air defence towers are close to each other or in the middle of the base. Balloons are very helpful in dragon attack specially in rage/heal attack. Balloons are used behind dragons to destroy the defences. They take cover from dragons and destroy the defenses. Level 6 balloons in the clan castle is recomended to use with dragon attack. You can also take a dragon as CC troops while attacking with dragons.

In the case of mass dragon attack you should be careful about the isolated buildings like buider huts situated at the end of a base. You’ll probably run out of time as dragons are pretty slow unit. You can take some barbarians and archers or minions with dragons. Use your barbarian king effectively to make sure you’ll get 100% of the enemy base.

Dragons are not used for farming purpose. Their training cost and training time is the reason. But they are widely used for trophy pushing to higher league. The first person to get to 4000 trpohies used all dragons to get to that position. He took 4 light spells. 1 to take out the clan castle troops and rest to destroy one air defence. Thus he ensured the 50% of that base.

Dragons are arguably the best unit for defence. For defending your village from th6 to th9 dragons do the best job. Dragons have area splash effect when they breathe fire and can defeat multiple units at a time. Dragons are completely immune to attacks from most of the ground troops. Giant barbarian attack can’t stand against a dragon in the clan castle. Besides their high hitpoint helps them to survive from archers/wizards for a long time while the defensive buildings can attack the enemy troops easily. An active barbarian king and a dragon defended base is critical to deal with. This is a good technique to save your dark elixirs.

To make an anti dragon base you should place your storages beside your air defences. And place your air defences semi spread. Place the high hit point buildings beside the air defences. Place your clan castle deep inside your base.