Apocalyptic Growlithe Line
The Apocalyptic Growlithe Line encompasses Apocalyptic Growlithe and Arcanine, which were released as part of the New Years 2015 event on the 1st January 2015 and are Exclusive Pokémon.
Regarding Double-Fire type: It's intentional. Regular Arcanine is already of the Fire type, so Apocalyptic Arcanine had to be extra strong effective. Hence the double Fire type.
Obtaining
Apocalyptic Growlithe can be obtained through breeding, trading, or the method outlined below.
<spoiler show="Show Method" hide="Hide Method">Breeding a Female Growlithe or Arcanine holding a Meteorite.</spoiler>
Event
The Apocalyptic Growlithe Line was one of 15 Exclusive Pokémon lines to be added in the New Years 2015 events.
Evolution Tree
Egg