Sports
1. Collect as many as 100x on any sportbets within a week, the highest person with the most 100x wins, minimum bet 1$. You can have the multi lower as a start to attract new sports bettor.
General/Casino
No further games here but a suggestion to increase the price. The current challenges are good enough but the prices are NOT anymore enticing. Imagine losing 30-100$ achieving a challenge and only get 3$ as a price after you hit it? Previously it was good since only few are participating, but then as the players increases trying the challenges, price also decreased tremendously, I suggest to increase the price as well, you have the data to back this up, I am sure it is not hard to calculate what will be the right amount.
Stake: PokerShame