When it destroys a monster by battle, it's able to gain an effect activatable in either player's Main Phase that lets you Tribute it to Special Summon 1 "Elemental HERO" Fusion Monster from your Extra Deck, ignoring its Summoning conditions
It also describes Pokmon TCG: Mega Evolution as a "series" - and in the same paragraph notes that Mega Evolution cards last appeared in the "XY series and Sun and Moon series" - suggesting that these new iterations will be released over the course of multiple Pokemon sets, and will likely be the main overarching theme for those sets
These dont have any holo foiling, special text, or textures to make them stand out
Despite its humble beginnings in the form of the useless Magikarp, Gyarados proves that there is always something more lurking beneath the surface
These are premium Charizard pieces that would be the crown jewel of most collections even if they do not quite reach the heights of the cards on the main list
Some sets are more viable than others, though, so its worth knowing where to spend your Pack Hourglasses