King Digital Entertainment, maker of the wildly popular mobile game Candy Crush, went public Wednesday morning on the New York Stock Exchange after raising about $500 million in an IPO that valued the company at about $7.6 billion. But it fell short of that valuation with a poor early response from the market, with shares opening at $20.50 — beneath the offer price of $22.50 — and falling still lower. It’s still a big win for the company’s founders and employees, but the company has a tall order ahead. The number of people who play Candy Crush, along with the sales and revenue it generates, have already begun to slow down and taper off. If it’s going to succeed as a public company, it will need to find a new source of momentum. The promise and peril of King’s business is a common phenomenon in the gaming industry.