This is how most mobile games work: Download the game for free. Build a virtual house. Wait. Sometimes for hours or even days. Build another house. Wait again. To skip the annoying waiting time, you need virtual money—so dole out real cash to buy in-game currencies. That’s essentially what the world’s biggest gaming company is doing.

China’s Tencent is nearing a deal to buy most of Finnish game maker Supercell at a valuation of more than $9 billion from Japanese telecommunications giant SoftBank, according to The Wall Street...