➥ Banner is something just like avatar, yet i haven't so far seen a cog to retrieve user banner. But look no further; this is the only cog for retrieving user banners you will ever need.
➥ [ OPTIONAL ] Run banner_embed to customize the embed holding the banner, or to disable the embed completely, and send the image as a normal message.
➥ banner <user>
➥ [user] is an optional argument. If you simply run banner, it will return your own banner.
➥ Currently theres no way to choose between guild/global banner of a user. I will add the option when the functionality to do so comes up.