Complex sentence: In actuality, the combination is not lethal, but could be very painful (as seen in the test of the myth on Mythbusters), and John Gilchrist, who played Mikey, is alive and well.
Split into simpler sentences: In actuality, though the combination can be somewhat painful (as seen in the test of the myth on "Mythbusters"), it is not lethal. Additionally, John Gilchrist, who played Mikey, is alive and well.