According to its file, Arcanine is described as being able to cover up to 6,200 miles within a full twenty-four hours. I can see the appeal in Arcanine being registered as transport pokemon, similar to how Lapras can ferry people across the seas and oceans on the back of its shell. I also don't see many people going bareback and saddles would be a must, both for the comfort of their trainers/travelers and itself.
Bullet here is still growing, so he looks a bit small, but once he reaches full maturity, he'll be over six feet at the shoulder, easily towering well over Lupin, who only stands at about five feet without boots or even paws. :D
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Art and characters belong to me~