More of a Game Graphics than a mechanics question

It's just highly unlikely that they're hand-crafting any of the sprites in the game.
It takes too much time.

You have to realise there is a team of artists devoted to things like this. Also Nexon AM takes a lot of their stuff from Korea. So I wouldn't say highly unlikely, more highly likely that they duplicate each sprite, adjust it to the angle/state they need it in and then clean it up by hand.