Espers are powerful beings that can be summoned by the player to help in battle. However, they must be defeated first and when they are, they will appear on the License Board. Players must now purchase them before they can use them, and they are exclusive to the character that purchased them.
Espers use Mist Cartridges, and there are three different tiers, with each tier using a different amount of cartridges (up to a maximum of three). When one of the characters summon one, the other two characters leave the battle, with the summoner remaining. Espers have their own Gambits and in the normal version of FFXII, they cannot be controlled.
They are nothing more than an extra character, as they can be buffed and healed by the summoner, although traps don't affect them. Espers will last a total of 90 seconds before they disappear, irregardless of battle speed, but there are other ways for an Esper to go away. If the summoner or Esper dies, they go away, as well as when they use their ultimate move (which has its own special criteria).
