Fire Lion is (hence the name) a lion coated in flames and is a mini-boss that has thus far appeared in three games in the Kirby series, Kirby's Adventure and its remake, Kirby: Nightmare in Dream Land, and later in Kirby Super Star Ultra. Fire Lion attacks by charging at Kirby in a stream of fire, and also by grabbing Kirby and scratching him, or trying to pounce on him. When Fire Lion pounces, a star will appear, allowing Kirby to inhale and spit it back at Fire Lion, inflicting damage. Fire Lion was extremely dangerous and aggressive in terms of attacking in Kirby's Adventure but has died down in its aggression over the years. In its original appearance, it looked very unthreatening and kitty-like, but later appearances drop the cute look in favor of a demonic appearance with a flaming yellow and red mane, and flaming eyes with no pupils.
In the Anime
In the anime, Fire Lion appears in the episode Junk Jam. Fire Lion is Nightmare's personal trash-burning demon beast. Upon being denied by Customer Service to have their alien garbage men stop dumping garbage on Dream Land until he pays his bills, King Dedede and Escargoon hack into Nightmare Enterprises' computer and ended up summoning Fire Lion in a plot to burn the trash that has piled up and covered Dream Land, but later fought against Kirby. When Fire Lion was downloaded, he went out of control and attacked King Dedede. He also spewed fireballs everywhere, especially at the trash. Before Fire Lion had the chance to destroy the rest of Cappy Town, Kirby was able to become Fire Kirby and battle him. When Fire Lion shot forth a large stream of fire, Kirby countered and overpowered it with his own fire. Kirby also had the chance to grab Fire Lion and fling him out to the sea. Fire Lion exploded when touching the water, destroying him.
In the Mario game Super Paper Mario, there is a tournament of which the challengers are samurai-like beings known as "Sammer Guys", each one's name referring to a thing in a Nintendo series (most often the Mario series). One of those Sammer Guys is called Molten Panther, possibly a reference to the Fire Lion.
In Kirby's Adventure, Fire Lion's artwork and in-game sprite depicts him as a seemingly normal lion with blue fur and saber teeth.