"This majestic creature lives to protect and aid her fellow troops. Any army is improved with her healing support, but make sure to protect her from air defenses!"
Level 1 & 2 Level 3 & 4
The Healer is a flying unit. She is the only troop with no attacking/offensive capability, but can heal any ground Troops, except when she is defending as a clan castle troop (in which case she heals damaged Clan Castle reinforcement troops and heroes).
When the Healer is deployed, a pulsating circular aura appears around her. If all units have full health, she will start healing the closest troops (although it will have no effect on the healed troops). Should a ground troop be damaged by a Defense, she will fly over and start healing.
Note that Healers will not heal flying units (other Healers, Dragons, Balloons, Minions, Lava Hounds or itself) unlike a Healing Spell which heals every kind of troop.
Note that Healers will heal Heroes at a reduced rate of only 50% of her normal healing rate; keep this in mind if you want to use Healers with your Heroes.
Healers cannot attack at all. They are completely unable to defend themselves, and will totally ignore any enemy buildings or troops attacking them. If they have no target to heal, they will simply remain stationary even if they are taking damage.
Unlike all other troops, healers are measured in (HPS): Heal per second NOT (DPS): Damage per second.
A Healer does not last long if she is in the range of an Air Defense, so make sure you destroy the Air Defense first or otherwise occupy them before sending in your Healer(s). One strategy is to send a few Wall Breakers in to break the wall that is protecting the Air Defense. Then send in a group of Giants (usually 12 or more) to destroy it. Finally send in a Healer along with other troops after the Giants. As long as the Healer does not get distracted by other Troops taking damage, or is not killed by a corner Archer Tower or Wizard Tower, the Giants will live for a significant amount of time (due to the constant healing) and will distract the defenses while the other troops destroy everything. This is known as a Giant-Healer raid and is extremely popular when attacking a Town Hall 6, since a Town Hall 6 only gets one Air Defense.
Another strategy is to use Balloons to tank the hits from an Air Defense. Since Balloons target defenses, there is a good chance that the Balloons will be closer to the Air Defense than the Healer. The Balloons may also destroy the Air Defense too.
If at any point in the battle all of your non-Healer Troops are killed and you have no more non-Healer troops or Lightning Spells/Earthquake Spells to deploy, the battle will end, even if you have Healers deployed that are still alive or non-Lightning/Earthquake Spells that are still in effect.
Healers can allow Giants and other defensive troops to withstand massive amounts of damage, even doubling that of their normal health.
Support durable Troops like Giants or P.E.K.K.As with Healers.
You are able to heal a Healer with a Healing Spell.
Healers do not last long if she is in range of a Single-Target defenses or an Air Defense, so make sure you upgrade and protect your Air Defense as much as possible.
Put your air defense in the middle of the base to prevent ground troops like Giants from destroying it quickly.
As of the 24 February 2015 update, the strategies to defend against Healers involving trap placement no longer work, as Healers do not trigger traps anymore.