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. Each crystal can be purchased in 4 versions: Mastery, Power, Endurance and Crit.

You can earn more then enough tokens each week to buy multiple crystals a week. However the Missions to earn tokens are related to playing SOLO, which means you cannot earn the tokens by playing with others in SOLO+!

However you can earn enough tokens by playing the Eternal Championship multiple times a week and completing the lowest-level Quest to reach round 5. Thus earning you multiple free Legacy crystals a week.