Barbarians have no preferred target when attacking; they will simply attack the closest building to them. However, once they become aware of enemy Clan Castletroops, Heroes or Skeleton Trap skeletons (either by being attacked themselves or being near another friendly troop under attack), they will leave their previously targeted building and engage the enemy troops instead. Once all of the nearby enemy troops are defeated, they will proceed to attack the nearest building from their current location.
Large hordes of Barbarians are very effective as they will quickly destroy anything in their path. This is balanced by the fact that the Barbarians are not very effective under heavy fire from splash damaging buildings. As such, players sometimes spread Barbarians to avoid them all being picked off in one group by a Mortar, Wizard Tower or Bomb Tower, as they deal splash damage.
Besides doing splash damage, the Mortar also knocks back any Barbarians it strikes by 2 tiles (sometimes this can even change the Barbarians' target, if it moves them closer to another building).
Barbarians can act as a "poor man's" distracting troop in a similar fashion to Giants; while they have far less health individually, a group of five Barbarians (the same housing requirement as one Giant) has approximately 75% of the health as a similar-level Giant (up to level 5) while doing nearly 4 times the damage (and costing approximately 20-25% of the Elixir to train). Note that this strategy is far less effective if splash damage defenses are in the area, as they will damage all Barbarians at once and destroy them relatively quickly.
They are good to take out lone buildings, like Builder's Huts placed far away to prevent full destruction.
If a Mortar is exposed and otherwise undefended, a single Barbarian can easily destroy it as Mortars cannot target troops which are within 4 tiles of them.
Barbarians, along with Archers, are normally used in swarms to defeat Barbarian King or the Archer Queen. This is because they are inexpensive, and take up the minimum amount of housing space and therefore can be deployed in large numbers; the fact that Hero attacks are single-target means that the Hero can only kill one of the swarming troops at a time.
Barbarians are effectively deployed with the Barbarian King once the King has received his Iron Fist ability. When activated, all nearby Barbarians (not just the ones summoned) will receive bonus speed and damage while they remain in the Barbarian King's circle of rage.
Barbarians are not too weak for Clan Castletroops as they have relatively high health and damage for single housing space troops. They are capable of soaking up a decent amount of damage, delaying attackers and allowing your fixed defenses to take care of the rest. Because their housing space is only 1, you will be able to have a large amount of them in your Clan Castle, making them more time consuming to lure out.
However, since the introduction of the Poison Spell, low-hitpoint units such as the Barbarian are significantly less effective inside Clan Castles.
The Barbarian undergoes significant changes at levels 5, 6 and 7.
Initially, the Barbarian appears to be a short, muscular man wearing a brown kilt with a leather belt and a steel shield-shaped buckle. He also has spiked wristbands on both arms, as well as a short claymore in his right hand. He wears a pair of leather sandals on his feet.
At level 3, the Barbarian gains a brown leather headband with an emblem on the center, and a bigger, longer claymore.
At level 5, the Barbarian’s headband is replaced with a horned helmet and his claymore turns into bronze.
At level 6, the Barbarian wields a dark iron claymore and sports a mightier horned helmet of a dark gray color and gray horns pointing downward, similar to that of the Master League symbol. All accouterments (kilt, belt, wristbands, and sandals) turn a darker shade of brown as well.
At level 7, the Barbarian replaces the dark claymore with a lighter-gray one that appears to be molten on each edge, and his horned helmet gains a gold accent along with gold horns. The spiked bracelets on his wrists turn black, and the spikes become gold.
Up to 20 Barbarians can be spawned when the Iron Fist ability of the Barbarian King has been activated. Both the Barbarians spawned and any other friendly Barbarians around the Barbarian King will be enraged.
Of the three troops that occupy only one housing space (Barbarian, Archer, Goblin), the Barbarian has the highest health and does the second-most damage (Goblins of similar level have higher damage per second). He is also the slowest-moving but fastest to train.
When you tap on an Army Camp, all the Barbarians stationed there will briefly raise their sword.
You can have a maximum of 240 Barbarians at one time in a complete set of fully upgraded Army Camps. This number increases to 275 if you include the 35 that can fit into a level 6 or higher Clan Castle. On the battlefield, you can clone an additional 80 Barbarians with two fully upgraded Clone Spells. You can also summon 22 additional Barbarians with a maximum-level Barbarian King.