One problem Zen here will have is the fact that the challenge games will have to be 75% luck which many players will avoid.
Non members can make 16% luck games!
If they use the 1v1 or 2v2 strategic template and don't customise there game will be 16% luck.
-> create a game -> built-in multi-player template -> All see templates of all sizes
Select, 1v1 strategic or 2v2 strategic, don't customize and you have a 16% luck game made by a non-member.