You can have it through Battle Pass by playing the game to earn XP and reach the tier 80.
The Battle Pass usually costs $10, $40 (for premium) or 1000 Coins (in game currency)
Yeah that's the reason that I farm and use Coins to buys it.
Actually, it's one of the worst system in F2P games. Almost Skin Pack wrapped in BP and hero paywall.
I'm not so positive about that, but at BlizzCon was announced some improvement of BP (S10 ahead?). Hope they make it more attractive and better for dedicated players.