Samuel Monroe Jr. showed a glimmer of hope amid his serious health battle ... but TMZ has learned the actor has experienced a severe downturn, as his condition continues to decline. Samuel's wife Shawna Stewart tells TMZ ... the "Menace II Society" actor is back on life support, in a medically induced coma ... and has required three blood transfusions in a matter of days, as his body is decimated by MRSA pneumonia and meningitis. He's been placed back on dialysis. The update is a devastating