If you are looking for ways to buy bitcoin anonymously, there are many ways to do it without the risk of using games credit.
For example, you can buy gift cards, pay with cash, sell them for a 5% discount.
Buying game credits is like buying Venezuela's currency, it is very central, difficult to convert into cash, and you may be banned at any time, so why use it?

It is also not an anonymous means as the game developers have full access to all your data, and if they accept fiat money without a license, the authorities will end up confiscating that game and losing your money.