Cobalion is a quadrupedal Pokémon that possesses traits of stags and goats. It is covered in aqua blue fur, and has jagged yellow horns similar in shape to thunderbolts. Its snout is a lighter shade of blue than the rest of its fur, and there a black blaze running from its nose to the back of its head. On its long neck and hind legs, there are small gray spots. It has a white tuft of fur under its neck, resembling a cravat. On its shoulder blades are yellow protrusions that resemble fins. Its tail resembles these protrusions, albeit in the same color as its snout. Cobalion's legs have black bands with lighter fur underneath and large black hooves.
Cobalion has a composed demeanor, but dislikes humans. Once, it fought against people to protect Pokémon. Its glare can make even an unruly Pokémon obey it.
In A Misunderstanding, Cobalion appears in the Mistralton Cave where his colleagues, Terrakion and Virizion, are being challenged by Trish of the Riches. Trish is startled into dropping her fire torches and causing a blaze inside the cave. The trio work together to put out the fire, then take Shoko and Trish's Pokémon away, only to give them back after persuasion from Black.
Pokémon Rumble Blast: Cobalion is the main antagonist for most of the game as he and his forces have been going around stealing Glowdrops from the towns for their own selfish reasons. It is later revealed he was gathering the Glowdrops to gain entrance into the now rusted World Axle, which takes a heavy toll on his legion as they all rust. With his forces now consumed by Dark Rust, Cobalion teams up with the player to infiltrate the World Axle, and ultimately defeats Dark Rust. After the player has defeated Terrakion and Virizion, they will be rewarded with this Cobalion who will be Rusty.
This Pokémon was unavailable prior to Generation V.
Of the Swords of Justice, Cobalion is the only one with a type immunity, the only one which has a double resistance, the only one whose English name is different from the official romanization of its Japanese name, and the only one whose French and German names differ from each other.
Cobalion appears to be based on the character of Athos from the novel The Three Musketeers. Like Athos, Cobalion is the oldest and the de facto leader of the group. Like the others of its trio, its appearance is based on ungulates. It bears close resemblance to a markhor (a type of goat) and species of antelope such as the greater kudu or eland. It also resembles a stag. Like the other members of its trio, its nose is shaped like that of a sheep or goat.
Cobalion and Cobalon are derived from cobalt (a metal and a color) and possibly stallion or champion.