:class:`Asset`:Returns an asset of the emoji, if it is custom.

def url(self):
        """:class:`Asset`:Returns an asset of the emoji, if it is custom."""
        if self.is_unicode_emoji():
            return Asset(self._state)

        _format = 'gif' if self.animated else 'png'
        url = "https://cdn.discordapp.com/emojis/{0.id}.{1}".format(self, _format)
        return Asset(self._state, url)