There is absolutely nothing about this Pokemon that is remarkable.
Of all the Pokemon that Nintendo could give away, a Mamoswine is probably the last one you would expect. It’s a fairly average Pokemon, the third evolution in a line of Pokemon that isn’t particularly iconic or fondly regarded either, and is generally considered a forgettable addition to the roster (although it is considered to be pretty useful in the metagame).
So it might appear to be slightly puzzling as to why Nintendo would give a shiny Level 50 Mamoswine away at the Pokemon European National Championships- although it does make sense from the perspective of it being a competitively viable Pokemon, and the Championships themselves being a competitive event. But yes, that’s what’s happening. Players who visit the Pokemon European National Championships this year (they don’t even have to be participating) will in fact get a level 50 shiny Mamoswine. The Level 50 Shiny Pokémon has the following moves: Icicle Spear, Earthquake, Icicle Crash and Rock Slide and the ability, Thick Fat.
The European tournament takes place in the UK later this month, with the world finals occurring in August in Washington D.C., USA.