In order to use this ability, the Beastmaster must have a pet active, obtained either via Charm or Call Beast.
While active, Charm status cannot wear off naturally. Since Familiar lasts for up to 30 minutes, a charmed pet will stay with the user for up to 30 minutes from the start of the charm, regardless of level difference. Pay close attention to the 'up to 30 minutes' part. It won't always last 30 minutes. Be careful.
Familiar only lasts for one pet. If the pet is defeated or lost in some other way (moving to another area, using Leave, etc.), Familiar is cancelled.
Familiar will not allow a pet summoned with Call Beast to stay summoned past its maximum time. (Example: DipperYuly will only stay summoned a maximum of 120 minutes. If Familiar is used 110 minutes after it was summoned, it will disappear 10 minutes later.)
This ability will boost a pet's HP by 10%. This applies to both charmed and called pets.
/ja Familiar <me>
Since Familiar is a one hour special, some people prefer not to make a macro for it to prevent unintentional activation.