"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 Buildings and Clan Castlereinforcement troops).
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.
A Healer does not last long if she is in the range of an Air Defense, so make sure you destroy or otherwise occupy the Air Defense 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, 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.
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 to deploy, the battle will end, even if you have Healers deployed that are still alive or non-Lightning 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.
You are able to heal a Healer with a Healing Spell, try for yourself!
If the Healer is donated as a Clan Castle reinforcement, she will heal buildings damaged by attackers as well as other clan castle troops.
If you are considering using a Healer in your Clan Castle for defensive purposes, it is strongly discouraged to do so. While Healers can and do heal buildings, in practice the amount the Healer can restore is far less than the buildings are taking, even from just a few Troops. Archers or other offensive troops are much better in this situation, as Healers really don't end up affecting anything given the time it takes them to heal and the fact that their large housing requirement (14) takes up most or all of the available Clan Castle space.
At level 3, her aura and her dress both turn from yellow to purple.
As part of the 23 May 2013 update, Healers had their training costs reduced at all levels, training time shortened from 20 minutes to 15, and required housing space lowered from 20 to 14.
You can have a maximum of 17 Healers at one time in a complete set of fully upgraded Army Camps. This number increases to 19 if you include the 2 that can fit into a level 5 or higher Clan Castle.
Note: Having this many Healers is highly discouraged as your army will have no offensive capabilities.