You get this for defeating Straga. Use the void walker on the floor windows then on Straga’s weapon arm. When he draws it back to strike jump threw the floor portal and appear on the platform behind him. Hit B when prompted then strike his face 6-7 times. Dodge kill the minions that spawn rinse and repeat. If you don’t dispatch of the minions fast enough he will do a swing across the screen you’ll have to jump glide over or dash fast back and clear.