Q: how they calculate the mid-range? Is there a random range?
A: when calculating the mid-range, we always take into account the current market volatility, meaning the game is playable at any volatility of the market. The mid-range is not a fixed percent of the BTC price. If it was, this would result in the price jumping from short to long too much and the game would be impossible to play.
Where do you get your prices from?, any specific exchange or maybe it's just average price of some different exchanges?, I think knowing that will give users some transparency and definitely will help with trust issue and eventually will lead you to gain more users for your website, also other trading pairs like ETH/USD are going to be added anytime in the future or it's going to be bitcoin only?