What is item "UMa5191"?

I saw that item onthisSerebii page while browsing around the Pokearth for Castelia City. Is that just an error on Serebii or is that item some scrapped, unreleased item? I remember seeing it on one of Castelia City’s buyable item section and it costs 50 Pokedollars. I think its a mail, but after seeing that it has its own page and it doesn’t redirect me to any mail page, I’m not sure about it anymore.

On the hyperlink above it can also be seen that it is only found in the Gen 5 games.

Pleaselog inorregisterto add a comment.

UMa refers to theabbreviation of the constellation, Ursa Major.UMa5191 in particular actually refers to an item in SWSH, not B2W2. The item being Dynamax Crystals, which are given through events that let the player spawn event Pokemon at Watchtower Lair. There are 300 different Dynamax Crystals, each with a naming format of a star, one of the abbreviations of IAU designated constellations, and a Harvard Revised number that identifies a star in that constellation in the Bright Star catalogue.

Sources:Bulbapedia list of Items in Gen VIII that includes the items with weird names(These items do not appear in the Gen V list)Dynamax Crystals:Bulbapedia/Serebii