This file was hosted on Mystery Gift Servers of Pokemon Bank, and is not accessible normally.
(The Pokemon Bank service retrieves the data from here, in order to give players the Mewnium Z)
However, it appears that Pokemon Bank changes the data when writing it to Pokemon Sun and Moon.
The most noticeable changes are:
Wonder card ID from 4 to 0
Wonder card color from Purple to Gold.
As there haven't been any other Pokemon Bank gifts in Generation 7,
it is not known if this change occurs for every wonder card that Pokemon Bank processes.
Internal name: present_n_0