Max Shutter speed
Panasonic GX8 can shoot continuously at max speed of
12.0 fps and has max shutter speed of
1/8000 sec. GX8 also has an electronic shutter which can shoot silently at max speed of
1/16000s. One thing to keep in mind is that electronic shutter may cause rolling shutter / jello effects, and also banding issues under artificial light on your images.
Flash
Unfortunately GX8 doesn't have a built-in flash but it has a flash shoe for mounting external flashes.
Focusing
Panasonic GX8 features a Contrast Detection autofocusing system. The AF system has 49 points to choose from. Panasonic GX8 also features
Face detection AF where it intelligently detects the faces in the frame and locks the focus automatically.
Post Focus
Panasonic GX8 has a special Post Focus mode which uses its 4K video and focus bracketing features together to shoot and stack a burst of images into a single image which you can change the focus point on the LCD screen after it is taken.