Complex sentence: Vsauce was a YouTube channel brand created by Internet personality Michael Stevens, who sadly passed away on the 8th Septemeber 2015 due to a heart attack, which is believed to have been caused by second hand smoke.
Split into simpler sentences: Vsauce was a YouTube channel brand created by Internet personality Michael Stevens. Who sadly passed away on the 8th Septemeber 2015 due to a heart attack, which Is beleived to be casued from second hand smoke.