This event was given away to commemorate The Year of Legendary Pokémon via Serial Code to players with a EU 3DS.
The gift received between Pokémon Sun & Moon and Pokémon Ultra Sun & Ultra Moon will slightly differ, in areas such as held item, level and moveset.
This Dialga can only received on Pokémon Moon & Ultra Moon, while it is normally able to be encountered the Ultra Space Wilds of Pokémon Ultra Sun.
Having it on the opposite game likely is to facilitate and help players encounter Giratina, as it has the requirement of needing both Dialga and Palkia to be in party.
Format Ver.1.0.6-1, Post Updated Date:20180203_2203
Format Ver.1.0.6-1, Post Updated Date:20180203_2204