Any website offering a direct 50MB or 500MB SeriousSam2.apk file is hosting fake, malicious software or adware.
Launch the app and grant storage permissions to load the data. README.md - aarcangeli/Serious-Sam-Android - GitHub download serious sam 2 for android
A flagship or mid-range Android device (Snapdragon processors with Adreno GPUs work best). At least 6GB–8GB of RAM. Any website offering a direct 50MB or 500MB SeriousSam2