This achievement can be found on the Crystal Clash Twitter
https://twitter.com/Rise_Of_Legions or by searching on Twitter itself for Crystal Clash. The in-game Twitter button at the main menu brings you to the more current Crystal Clash page which does not seem to have the code listed.
To unlock this achievement head over to the shop in-game. Click on redeem bonus code and then copy and paste or type out in all caps in the box. Once done hit enter for an achievement.
XXYX-R0F7-TW1T-T3RX-YZXX