It's the Champion's Ballad DLC. When you complete the 4th divine beast, Zelda will tell you to go the the Shrine of Resurrection. When you get there, Maz Koshia will give you the One-Hit Obliterator and make you kill monsters.
Which sucks.
I have had the most embarrassing deaths because of the One-Hit Obliterator -
Killed by a Red Bokoblin with a Korok Leaf... Kicked to death by a Moblin... Fell five meters to my doom...
Then he makes you do a bunch of other stuff, including shrines, killing the blights AGAIN but this time without any good stuff, and then fight him.
But your reward is the Master Cycle Zero.
Caption this Meme
