It appears to be a crossbow with wooden and rock features, blue-grey plastic bottom parts and a shining steel bolt which is its ammo. A rope pulls it behind with each hastened shot.
An X-Bow can destroy a Crown Tower single-handedly if it's ignored by the opposing player.
An X-Bow is a powerful defensive building due to its extremely long range and ability to take down large numbers of weak troops such as Goblins, Spear Goblins, and Skeletons. When defending, you can place the X-Bow behind or between your Crown Towers as it will be well protected but still able to engage attacking enemy troops from afar.
It can also be used offensively due to its range, being able to out-range the Crown Towers, making for some extremely humorous battles (11.5 vs. 8.5 tile range). Note that the Mortar can also outrange Crown Towers, but it deals significantly lower damage per second, has a slower fire rate, has a slightly shorter range (11 tiles), and does Area Damage.
The Rocket is the most reliable and effective counter to the X-Bow due to the fact that the Rocket almost obliterates it immediately, letting the X-Bow only take a few shots. The Rocket can also destroy or cripple common X-Bow defences like Archers, Knight, Minions, Bowler and Goblin Gang.
Building targeting troops like the Giant and Hog Rider are not distracted by X-Bow defences and can pummel the X-Bow to it's destruction while air troops like Minions, Mega Minion and Baby Dragon can harass it as the X-Bow cannot target air. Balloon is a powerful mix and paired with it's high damage is probably the most reliable troop to counter X-Bow.
An X-Bow takes 3.5 seconds to deploy, leaving you ample time to place a tank and dps cards behind to quickly deal with the X-Bow and any defending units. This attack can be turned into a full on push to punish the opponent.
An X-Bow backed up with some support troops or buildings, such as Archers or a Tesla can destroy a Crown Tower. Place the X-Bow behind or near such cards so that it will be protected while it destroys the opposing Crown Tower. It is advised to tank for the X-Bow so it does not take the brunt of an attack so it can carry on chipping away at the tower.
If you just miss your timing for a distraction and the X-Bow is locked on to your Crown Tower then a Zap will force the X-Bow to re-target to the nearest entity, which is hopefully a tank so you're damage dealers can safely destroy the X-Bow.
When dealing with an offensively placed X-Bow, it's quite effective to deploy a Musketeer behind the river/chasm while the X-Bow is deploying, taking out a large portion of its hitpoints before it's ready to fire.
However, be aware of opposing defensive buildings/troops next to the X-Bow, as they will take down the Musketeer quickly if she is in a bad position.
To protect the Musketeer, it is advised to place a tank such as an Ice Golem in front of the Musketeer to absorb any incoming fire from enemy troops, buildings, or the X-Bow itself.
Casting a Rage on an X-Bow will increase its hit speed, rapidly inflicting damage to the targeted unit/Crown Tower, and will boost the player's troops defending the X-Bow. However, the Rage will also reduce the X-Bow's lifetime. Note that this costs 8 Elixir, which is very risky to play!
It's wise to deploy it alongside a card with a good amount of hitpoints (the Knight) or a swarm card (Skeleton Army), as they can slow down enemy troops sent to destroy the X-Bow.
The Bowler is a great counter to X-Bow since it will hit the X-Bow and the any defending units, resulting in a positive Elixir trade.
When facing an X-Bow, always try to go for the first crown and then the 2-1 victory. If you take down a tower, it will be very difficult for your opponent to take down the tower facing your enemy's destroyed tower (provided your tower is still healthy), because with the extra terrain you gain from taking down an enemy tower, you will be able to place troops directly on top of the X-Bow attacking your healthy tower, allowing for defending troops to immediately start doing damage to the X-Bow without having to walk, deal with tanks, and have a bad position in general. This works particularly well with Splash Troops, such as the Valkyrie, as if it is placed on top of the X-Bow, no matter what your opponent places down, your Valkyrie will start damaging the X-Bow and at the same time tanking. With appropriate anti-air/splash support, the X-Bow, taking tons of splash damage, will be quickly annihilated.
The X-Bow was released with Clash Royale's soft launch on 4/1/16.
On 2/2/16, the February 2016 Update decreased the X-Bow's hitpoints by 15% and now only targets ground (from air & ground).
On 23/3/16, a Balance Update decreased the X-Bow's range to 12 (from 13).
On 3/5/16, the May 2016 Update fixed the "range bug" and decreased the X-Bow's range to 11.5 (from 12) but its effective range is unchanged.
On 21/6/16, a Balance Update decreased the X-Bow's deploy time to 4 sec (from 5 sec) and increased its hitpoints by 18%.
On 11/8/17, a Balance Update decreased the X-Bow's deploy time to 3.5 sec (from 4 sec).
The X-Bow is the only Epic building in the game and has the highest rarity out of all the buildings in the game.
At tournament levels, a Rocket almost completely destroys an X-Bow. If the Rocket is four levels higher than the X-Bow (one level higher than the equivalent level), it will one-shot the X-Bow.
The X-Bow has the longest range of any card in the game.
The X-Bow is the fastest retargeting card in the game.
The X-Bow and the Mortar have the longest deployment time of all cards in the game clocking in at 3.5 seconds.
The X-Bow, Mortar, and Princess are the only cards that can target Arena Towers without getting targeted by it.
The X-Bow has the fastest hit speed of all cards in the game, at 0.25 seconds. Because of this, the X-Bow deals the least amount of damage per hit of any card in the entire game, taking multiple shots to kill even Skeletons.
In Clash Royale, the X-Bow can only target ground units, while in Clash of Clans it can be set to ground mode or ground & air mode.
However, the X-Bow was originally able to target air in Clash Royale.
It also shoots Elixir bolts in Clash of Clans, while in Clash Royale it shoots crossbow bolts.
It can shoot 160 bolts in its lifetime, dealing a total of 6080 hitpoints in damage at level 8, which is enough to fully destroy a level 13 King's Tower.
The X-Bow's description is a reference to a meme known as "Nice X you got there. Would be a shame if something happened to it."