Ok I made it by upgrading Retropie to 3.2 which is using fba Next by default. This emulator is much better and I'm now able to reach toggle menu, set Unibios available and change geographic zone on rom boot.

All metal slug are now working properly with people full of red blood

Hi everyone, For your information, I managed to run Metal Slug 1, X, 3, 4, 5 properly on Raspberry PI 2 powered by Retropie. Sound is working properly and action is smooth (at least level 1 for each games, I haven't played more so far). I can share BIOS and other stuff if required. I spent almost 2 ...