Ultimation

The "Ultimation" is a war machine with various elemental abilities created by Lian.

History
Once Team Avatar arrived at the fortress where Lian was located, the latter called out to the missing benders the team had been looking for, who revealed themselves apparently willing to aid her by powering the "Ultimation".

Team Avatar's united attacks managed to put down the machine, but as Aang got distracted, the Ultimation attempted to attack him from behind. Katara got in the way to protect Aang, but got hit by the Ultimation, rendering her unconscious. Enraged, Aang went into the Avatar State and easily destroyed the machine, making it topple over Lian.