Terrakion is a bovine, quadruped Pokémon. It has a black, rounded forehead adorned with two sharp brown horns that curve forward. Its face is beige with orange eyes and short snout. On top of its head are several short spikes. Down its back are two brown ridges that join just past its shoulders. There are two orange protrusions on its shoulders. The bands around its legs are the same color as its face, and it has black hooves underneath these bands. Its striped underside is also beige. It has a short, stubby tail.
Terrakion fought humans alongside the other Swords of Justice during a war with humans in order to protect Pokémon. It is strong enough to destroy a castle wall in one blow.
Terrakion appears alongside Virizion inside Mistralton Cave in A Week to Go and Old Wounds, where they are challenged by Trish of the Riches, as well as Black. Just as they appear to be losing the battle, their leader, Cobalion, appears, and startles Trish into dropping her fire torches and setting the cave ablaze.
Terrakion is similar to Moltres in three ways: it is a member of a non-mascot Legendary trio, is found in its region's Victory Road in the first games that feature its region, and is found in a different location in all subsequent games.
Terrakion takes supereffective damage from Grass, Steel, Water, and Fighting; the collective types of the other members of its quartet.
Terrakion appears to be based on the character of Porthos from the novel The Three Musketeers. Like Porthos, Terrakion is the heaviest, largest, and strongest member of the trio. It also has traits of big horn sheep and oxen. Like the other members of its trio, its nose resembles that of a sheep, goat, or other hoofed animal.
Terrakion may be a combination of terra (Latin for earth) or terracotta (a clay-based material, as well as its respective color) and takin or champion.