The Poison card is unlocked from the Spell Valley (Arena 5). It is an area damage spell with a fairly wide radius and moderate damage. It creates a circular area in which troops and buildings are damaged slowly over time. It is a deep orange liquid in a thin oblong vial. A Poison card costs 4 Elixir to cast.
- Unlike the Fireball, the Poison's damage is capable of fully defeating a Musketeer, Wizard, or Electro Wizard, but these troops tend to walk out of the radius before the spell's full damage can be dealt. To solve this, the player can place any troop nearby the troop that is just about the walk out of the Poison's radius. This will distract them and make them stop moving, keeping them inside the radius.
- Poison can replace a Fireball if it is preferred to cripple anything in a larger radius. The only disadvantage is that the player won't be able to deal high damage to enemies immediately.
- The Poison's long duration allows it to deny swarm cards from being effectively used inside its radius. This can be useful on offense after sending in a troop that only targets buildings or a troop that can only attack one unit at a time, as the spell will often force a less practical counter out of the opponent. However, its damage on spawning units is not instantaneous, so swarms that can survive its first tick will still be able to land a hit or two. This is also does not work nearly as well against Barbarians, as their higher health allows them to still do massive damage before being taken out (albeit for a positive Elixir trade).
- Poison is one of the more efficient methods at dealing with buildings that spawn troops, as the spell will not only reduce the building's lifetimer but also damage down the oncoming units. This works just as well against Witch and Night Witch, limiting their damage output and leaving them at critical health.
- Poison cannot one-shot Skeletons 2 levels above it, so players should make sure their Poison is sufficiently upgraded.
- Poison can be a consistent counter to the Graveyard, sharing a similar duration while covering most of its radius. However, a few Skeletons will still manage to damage the Arena Tower. These properties also make Poison pair well with the Graveyard as it will quickly defeat any low health troops that are trying to defend against the Graveyard.
- Poison pairs well with the Miner, as its ability to deny swarms for a lengthy amount of time can allow the Miner to deal considerable chip damage uninterrupted. However, this combo is fairly ineffective against cheap tanks like the Knight. Despite this, the mere threat of a Poison spell along with the ambiguity of the Miner's placement will often force the defender to commit a single tank to one spot, rather than them using a swarm to cover multiple placements. If they guess incorrectly, the Miner will still deal some chip damage while not leaving the attacker at a large Elixir deficit.
- The Poison was added to the game on 29/2/16 with the March 2016 Update.
- On 23/3/16, a Balance Update increased the Poison's damage by 5%.
- On 3/5/16, the May 2016 Update changed the description of the Poison. The description prior to this update was "Covers the target area in a sticky toxin, damaging and slowing down troops and buildings. Remember: solvent abuse can kill!"
- On 20/10/16, a Balance Update removed the slowing capabilities of the Poison. This also changed the description. It was used to say: "Covers the target area in a sticky toxin, damaging and slowing down enemy troops and buildings. Yet somehow leaves the grass green and healthy. Go figure!"
- On 30/11/16, a Balance Update increased its damage by 10%.
- On 13/2/17, a Balance Update decreased its duration to 8 seconds (from 10 seconds), but increased its damage per second by 24%.
- On 12/6/17, a Balance Update allowed multiple Poisons to stack.
- On 12/12/17, a Balance Update decreased the Poison’s Crown Tower damage to 35% of the total damage (from 40%).
- On 4/8/20, a Balance Update decreased the Poison’s Crown Tower damage to 30% of the full damage (from 35%).
- The Poison uses the same deployment and sound animation in Clash of Clans.
- It is one of two direct damage spell cards that does not contain the phrase "Reduced damage to Crown Towers." in its description despite dealing reduced damage to Crown Towers, the other being The Log.
- Poison’s effect stays with troops for slightly after they leave the spell’s duration, which is best seen when poisoning a Fast flying troop.
- In Clash of Clans, Poison also slows movement speed and hit speed of affected troops, but does not affect buildings.