Did you know that you can obtain purple, cyan or magenta crystals that are legacy bound, for every stat type in max +41 stat?
They cost 2 Medals each from the Eternal Championship vendor! All you need to play the minigame is access to Zakuul + at least KOTFE chapter 9 complete.

You can earn more then enough tokens each week to buy multiple crystals a week. As there are quests related to playing Solo, with friends and reaching bosses at certain waves before leaving the minigame!