Aethersprites are able to attack (and heal) Invisible characters.
An Aethersprite will only attack characters of Evil alignment, unless their master possesses the Hand of Zealotry skill (in which case they will attack Neutral characters as well) or the Holier Than Thou skill (in which case they will attack anyone of lesser Morality than their master).
Aethersprite behavior is different from that of most other pets. They are primarily concerned with the health and safety of the Lightspeaker who summoned them, and will heal him first before attacking. On the "10-second" tick, Aethersprites always try to heal in lieu of attacking, and will still heal when set to passive (Aethersprite healing does not grant XP). Aethersprite heals restore 10 hit points and remove Minor Poison, Defiler Poison, and Enervated status effects if they heal a character. Sorcerer's Might prevents Aethersprites from even trying to heal (Aethersprites cannot reduce Sorcerer's Might duration), while the Glyph of Pain vs. Good prevents the Aethersprites from healing anybody except for their master. Characters affected by Blood Curse cannot be healed by Aethersprites.
If the Lightspeaker possesses the skill Heart Light, when an Aethersprite heals it also transfers 5 MP from itself to the charcter, up to the target's normal MP maximum. This only applies to characters other than the Aethersprite's master.
On a "retaliatory" tick, Aethersprites have a 10% chance of healing in lieu of attacking.
If an Aethersprite heals, it expends 5 MP and 1 AP. If an Aethersprite tries to heal, and can heal its master, it will. If its master cannot be healed (or does not need healing), it will heal a random character of good morality in the location. If there are no good characters in the area that the sprite can heal, it will attack. Aethersprites can heal good-morality demons.
It is important to note that while Aethersprites can target and attack invisible characters, they cannot heal any invisible characters of good morality in their immediate location.
An Aethersprite stolen by Touch of Corrupted Loyalty loses its healing abilities and becomes known as a Hellsprite.