Tesla

“Defensive building. Whenever it's not zapping the enemy, the power of Electrickery is best kept grounded.”

The Tesla card is unlocked from the P.E.K.K.A.'s Playhouse (Arena 4). It is a single-target, medium-ranged defensive building with both moderate hitpoints and damage. When not attacking, the Tesla will retreat underground, invulnerable to any damage. However, its lifetime and hitpoints will still decrease. A Tesla card costs 4 Elixir to deploy.

Strategy

The Tesla can zap away some health from moderate hitpoint troops at a decent rate. It also deals moderate damage to higher hitpoint troops such as the Baby Dragon, and can also take out a Lava Hound and its pups without any assistance.
The Tesla can kill Minions, Goblins, Spear Goblins, Fire Spirits, Bats and Skeletons in one shot, thus making it very effective against small hordes of troops.
When it retreats underground, the Tesla is invulnerable to any damage-dealing spell such as the Rocket and Lightning, and cannot be targeted by any troops. However, the retreat is not instant, enabling quick troops like Spear Goblins to get a hit off before it goes underground. The retreat can also be stopped with a Freeze spell, enabling the player to attack the Tesla at leisure.
The Tesla can be frozen by a Freeze spell while underground, so it won't pop up when enemies are in range while the Freeze is active on it. This allows troops such as the Hog Rider to bypass a Tesla and head straight for the Crown Tower, as it can't be targeted while hidden underground.
Although the Tesla has the same range as a Cannon, it can still target troops that would normally outrange it due to its ability to become invulnerable when not attacking, forcing them to come into its targeting range before they can target it. Thus, when using long-range units, the player should provoke the Tesla with another troop first to prevent the long-range troop(s) from wandering into its range and being destroyed.
The Tesla is great at distracting enemy troops that target buildings, such as the Giant and Hog Rider. By placing it in the middle of the player's part of Arena, the troops will target it instead of the Towers if it is not frozen.
The Tesla's re-targeting is rather slow, meaning that the player should send troops in swarms of units when attacking an enemy's Tesla (like the Skeleton Army). However, this can be easily countered by splash damage cards.
The Tesla can target both air and ground troops and has a smaller hitbox. It also has more health and damage, so it can be interchangeable with the Cannon. However, it costs 1 more Elixir to deploy.
Unlike other buildings, the Tesla takes up a 2x2 space as opposed to a 3x3 space. This means that it can fit in the gap between a Princess Tower and the edge of the Arena.
It can support siege buildings like X-Bows or Mortars from your side of the Arena.
A Tesla is interchangeable with the Inferno Tower, especially in Log Bait decks, as it provides high damage while costing 1 less Elixir.

History

The Tesla was added with Clash Royale's soft launch on 4/1/16.
On 9/2/16, the Chest Rewards & Card Balance Update increased the Tesla's damage by 7%.
On 29/2/16, the March 2016 Update decreased the Tesla's hitpoints by 5%.
On 23/3/16, a Balance Update decreased the Tesla's hit speed to 0.8 sec (from 0.7 sec) and its lifetime to 40 sec (from 60 sec).
On 3/5/16, the May 2016 Update fixed the "range bug" and decreased the Tesla's range to 5.5 (from 6) but its effective range is unchanged.
On 18/5/16, a Balance Update increased the Tesla's hitpoints by 5%.
On 21/6/16, a Balance Update increased the Tesla's hitpoints by 8%.
On 9/10/17, the October 2017 Update increased the Tesla's damage by 41% but decreased its hit speed to 1 sec (from 0.8 sec).

Trivia

The Tesla's mechanics are similar to its counterpart in Clash of Clans, the level 1 Hidden Tesla which it resembles. However, in Clash of Clans, the Tesla does not retreat underground when it is not actively attacking; it simply remains above ground for the rest of the attack.
The Tesla is the only defense that can be placed symmetrically.
The Tesla is the smallest building in the game.
It is named after the Tesla coil, a device invented by Nikola Tesla which can produce large amounts of AC current in frightening display. However, despite its name the Tesla does not include the namesake device in Clash Royale.
The Tesla is the only building which retreats underground when it finishes attacking.
The word 'electrickery' is a play on words, and a reference to the Tesla's description in Clash of Clans.
If the Tesla is about to retreat and the Freeze is used on it, the retreating sound effect will loop.
The Tesla and the Inferno Tower are currently the only buildings that can hit air troops.