The first part of this Pokémon's name is a reference to the word Terra, meaning Earth, referencing the fact that it is a Rock-type Pokémon, as well as the Pokémon's color; Terracotta, a shade of brown.
In Pokemon Black and White it can only be reached by entering the end of Victory Road by moving the boulder. After moving the boulder, you can reach its trial from the North or South.
This is no longer the case in Pokemon Black 2 and White 2 as that part of Vicotry Road caved in during the 2 year timeskip and it is now found on Route 22.
Terrakion is the only legendary musketeer to have a unique type combination: Cobalion has the same combination as Lucario, Virizion has the same combination as Breloom, and Keldeo has the same combination as Poliwrath.
Terrakion is one of the two legendary Pokémon that is found in Victory Road in the generation it was introduced, the other Pokémon being Moltres.