This event was distributed to those who purchased a 20th Anniversary Pokemon Clear 2DS (Red/Blue/Green/Yellow) from Japan,
that came bundled with a collection ticket see screenshot area.
The device also comes with a code card for a Serial Code for Mew, a code card for the respective theme, themed stickers , and pre-loaded with the Virtual Console title.
(The event is received in real life between March 19 to May 8, 2016. It can have any date on the PK7, due to transporter applying a date whenever it is transferred.)
The ticket would have to be taken to a participating Pokemon Center in Japan, in order to receive the Mew via trade.
As the DVs (Gen I IVs) are distributed with 15 in every slot,
it is not possible to obtain this as a Shiny when transferred normally through Pokemon Transporter.
This PK1 file will only be compatible with JPN version of the game.
This is a video of my friends helping me to collect the Mew event!
(audio got muted by youtube due to proprietary song playing in the background)