Unlimited artwork unlocks question

I am curious how one goes about unlocking these, I thought it would be something simple like earning some cash and then buying them from the store, that isn’t it. Figured maybe it was beating arcade on hard or above, that wasn’t it. Maybe some online matches with the character you want the art for. Well 30 matches later, nothing. But I see people online with scores of 0-9 and they have it. So how exactly do you go about unlocking these things.

Ghost Battles

when u get 2 decide who u wanna fight next if one of the chioces is shining choose that 1

sweet thanks for the help.