The Zap can also be used to temporarily stun Balloons from reaching your Arena Tower, giving the defending player's Crown Towers and troops a little more time to eliminate the Balloon.
Zapping units or the opposing Crown Tower can possibly change their targets. For example, if an X-Bow is targeting a Tower and the player deploys a troop or building closer to the X-Bow than the Tower, then zaps the X-Bow, it will change targets to the nearest deployed card.
The Hog Rider + Zap combo utilizes the Zap to stop most cheap troops (or to stun defending troops) that are played to take out the Hog Rider.
With proper timing, Zap can be used to deny a wave from troop spawners such as Barbarian Hut or Goblin Hut, allowing the player to gain a small Elixir advantage. The same strategy can also be used against Elixir Collectors, as it will deny 2 Elixir if timed just correctly, but this is an even Elixir trade.
The Zap inflicts area damage similar to the Arrows. As such, the Zap can also be an alternative to Arrows, as it inflicts slightly less damage and a brief stun in a small area at the cost of 2 Elixir, as opposed to the Arrows' Elixir cost of 3.
The Zap was added with Clash Royale's soft launch on 4/1/16.
On 19/2/16, the Balance Update decreased the Zap's Crown Tower damage by 20%.
On 29/2/16, the March 2016 Update added a stun effect to affected targets in the Zap's AoE (Area of Effect) for 1 second and decreased its damage by 6%. The update also changed the description from "Lightning zaps enemies, dealing damage inside a small radius. Reduced damage to Crown Towers." to the current description.
On 24/8/16, a Balance Update decreased the Zap's stun from 1 second to 0.5 seconds.
It also does the same damage as the Electro Wizard's spawn damage 8 levels lower.
Lightning and Zap are two completely different spells, even though they have similar effects and visual appearances. The Zap deals less damage than the Lightning, but it has a much lower Elixir cost and does area damage. The Zap and Lightning are the only spells in the game that could stun buildings or troops.