"Death’s Scythe, the Harvester, boasts a blade that resembles a barbed wing – a fitting shape, for new weapons cut through the air with more and more life-ending precision. This fabled weapon was made many years ago, to fill the bony hands of the Horseman Death.
The scythe slices in great arcs, harvesting bushels of heads and gallons of blood. Even the intangible shades of Hell part like acrid vapor against its greedy edge. From death, there is no escape."
However, this is found to be not exclusive because anyone who followed the instructions is able to unlock the scythe as well, as elaborated by Seth from BOB.
Be warned though, as highlighted by pizzabit, that if you have the normal scythe already, any progress made using that weapon will reset and you will end with a cool looking scythe that deals lesser damage than the one you already had.