If you want a polished, native mobile experience that feels like Left 4 Dead 2 but is built for Android, several "clones" offer excellent offline gameplay:
Several independent developers have created "Mobile Ports" that attempt to recreate the game's assets and gameplay loop. These are typically available as APK files from third-party hosting sites: Left 4 Dead 2 (L4D2): Mobile by RPG GAME left 4 dead 2 download offline android
So, you’ve decided to go with Nillerusr’s port. Here is how to ensure a smooth experience. If you want a polished, native mobile experience