Mew ex has been popping up in all sorts of competitive decks for over a year, and since most decks only run one copy, players feel tempted to make that copy as shiny as possible
Normally, Universes Beyond cards are reprinted with more MTG-appropriate art and names at a later date under the Universes Within imprint
This can be further exploited by utilizing Chandelure's ability Alluring Light, which forces both the player and their opponent to draw more cards, thereby allowing Chandelure's damage output to continue rising
and in a lot of cases the unlimited edition print runs are much rarer and harder to find than their 1st edition print run counterparts
Looking at the details it seems like the artist, Reddit user Lord-Keithulhu, carved into the cards themselves to further create depth and features that take this alter to the next level
Returning it to hand, banishing it, or even using it as synchro material (as unlikely as that is), all of it counts