I'll try to keep this as short as possible and start from the beginning for anyone who's completely lost.
Someone posted a private video through Snapchat containing the
entire mural and an alternative version containing no characters. It contains 7 new fighters. The recipient of this message took snapshots of the video and posted them to 4chan There are instructions for the material which ties it to promotional printing (or potentially
an armband?), alongside other hints;
- Additional renders of the Grinch and some form of instructions for the upcoming new movie. They seem to be unique.
- AUTOCAD commands seen in the snapshot. This has led to this infographic.
- The employee's name was uncovered, which led to his LinkedIn profile; he works in promotional printing and graphic design.
Many believed he worked at a printing company called Marina PLV, spread by
this infographic which details the consistency of this leak and its ties to the company.
They gave a statement that he left in 2016 and they have no relation. This news is what caused many to think the leak may be fake.
However, he has an additional LinkedIn page that lists his current work in ACP PLV for about 1 year and 8 months; it fits with his leave at Marina PLV.
NintendoActu has claimed that they called his current workplace and can confirm that he does indeed work there.
Liam Robertson is claiming that the suspected person has denied any involvement with this leak.
There are a few inconsistencies people have noticed such as differences in battlefield's backdrop design, but inconsistencies have already been created
via official material.
edit: fixed link.