Despite being the OU Pokemon, it is untiered on Smogon because it is not one of the Fakemons from CAP to make it to the battle simulator (being Pokemon Showdown which includes the CAP Fakemon such as Pajantom or Syclant) Smogon uses. If it was tiered it would be in BL due to having a high speed stat and Spore.
Despite being the OU Pokemon, it is based on Talonflame who is no longer in OU due to the Gale Wings nerf and not having Gale Wings as an ability.
Smoxilon and its pre-evolution Smogaroben are based on Smogon. Smoxilon is a purple Talonflame with a Koffing as its head with a gaseous tail. Its movepool also consists of moves commonly used on Smogon sets (Stealth Rock, Scald, etc.) and its species being the OU Pokémon is an obvious reference to Smogon's OU tier.