Nice, don't transfer it for the moment, we need data before catching.
Plus, do you accept to let @theSLAYER have an access to your account to get that Gengar later?
PKHeX uses this site's event gallery to validate mystery gift encounters; if it's not in the repo then PKHeX doesn't know about it
PKHeX checks for 100% matches for gifts... would have to be contributed (or added fake-legal gift data) for it to be recognized!