The Firebird is an elemental spirit residing inside the Mount St. Helens volcano who appeared in the Disney vs. Non-Disney Villains war.
First appearing the Disney animated film Fantasia 2000, the Firebird played a similar role as the earlier Chernabog, being the antagonist of the Firebird Suite segment of the movie.
Disney Vs Non-Disney Villains War
Battle of the Spirits
Summoned by Hades, as his new champion, the Firebird takes on the demonic spirit, Hexxus, as the latter dethroned Hades from his position, as God of the Underworld. While the Firebird manages to strip Hexxus from most of his powers, the spirit returns again, assuming his real form. Together, Hades and the Firebird combined their strenght to reseal Hexxus in a tree, in which it was originally imprisoned from within, defeating him. The Firebird does not make another appearance in the war, thus his fate remains currently unknown.
Disney Villains War
The Firebird appears as a servant of Chernabog's inner circle, contributing the Black God's effort for mass genocide and plunging the world into total chaos. It is defeated by hero alliance, as Hades and Odin combine their powers to weaken the villains, though at the cost of their sanity. The Firebird remains uninterested in the war of the villains, that follows, until it is invoked by the Black God's remain servants.
Fire Vs Rock
During the events of the war, Dr. Facilier, Chernabog's trusted lieutenant, summons the Firebird to take on one of Hades' Titans, the Rock Titan. Squaring off with the rock monster, the Firebird shoots his flame breath on the Rock Titan's back, though it did not harm him in any way. When the Firebird gets closed in, the Titan tosses a boulder upon the spirit, dismembering it. However, the Firebird reassembles and takes on the Titan with brute force. The spirit destroys the Titan's rock heads, before it proceeds to destroy the Titan itself. The Firebird does not make another appearance afterwards.