This clever pairing weaponizes a classic lifegain effect by letting Tainted Remedy intercept Beacon of Immortality right as it resolves. Normally, doubling an opponent's life total would just make them harder to defeat, but Tainted Remedy inverts that life gain into direct life loss instead. Because the Beacon of Immortality doubles their exact life total and the replacement effect turns all of that gained life into damage, your unfortunate opponent takes damage equal to their entire life total in one fell swoop, instantly dropping them to zero life.