Growstars are used for augmentation from 3 to 4 , yes 5 use different farmable ! materials . Due to the slow rate of acquiring Growstars one per month from the Mobius box , two per month from login rewards , 4 every time you ' ve saved up enough for the 4 pack and maybe rarely from events they end up being the bottleneck for upgrading your key cards , so they are very valuable and should never be squandered . You probably don ' t really need any 4 cards at the moment , anyways . Keep playing for a while and get some info before choosing your augments . Currently , no AoEcone ability is worth augmenting to 4 , and the single target abilities are not worthwhile either because you can get 4 single target cards without spending Growstars from multiplayer .