Theres a few different classes of cards so lets dive into each of them
Ardyn, the Usurper Braska's Final Aeon Cecil, Dark Knight Deadly Embrace Galian Beast Golbez, Crystal Collector Jecht, Reluctant Guardian Jenova, Ancient Calamity Kain, Traitorous Dragoon Kuja, Genome Sorcerer Midgar, City of Mako Ninja's Blades Noctis, Prince of Lucis Seymour Flux Shinryu, Transcendent Rival Sin, Spira's Punishment Squall, SeeD Mercenary Summon: Primal Odin The Darkness Crystal Trance Kuja, Fate Defied Vincent Valentine Xande, Dark Mage Zenos yae Galvus Zodiark, Umbral God
Mana Vortex Mana Vortex is a weird card
While they have always been swapped and collected, the cards' value have exploded in recent years, not just among fans of the game but also among investors with little or no past interest