Mason challenge requires you to raise the promotion_requirement of each ladder by at least 50% (except AH-ladder).
This challenge essentially makes you a true active waller and might be hard to pull-off in early game but should become easier with time and progression since during the mid-game rankers become more spread and start saving their vinegar for AH-ladder.
Winning the round is possible but is quite hard due to walling taking a good bit of time, especially if you are being thrown down a lot.