When an Android device starts exhibiting issues like frequent crashes and rapid battery drain after downloading an application, the first step should be to address the immediate cause:

Uninstall the game application: Since the issues started after the game application was installed, removing it is a logical first step. Unwanted or malicious applications can cause such symptoms by running harmful processes in the background or exploiting system resources.

Install the latest security patches: Keeping the device updated with the latest security patches is crucial for protecting against vulnerabilities that could be exploited by malicious software. Updating can resolve existing security flaws and improve device stability.