Elden Ring PC | Black Knife Assassin boss fight in Sage's Cave, co-op w/1 summoned player on NG

Drops:
6,750 runes
Concealing Veil

Black Knife Assassin
"Black Knife Assassins are Bosses in Elden Ring. This Elden Ring Black Knife Assassin Guide features boss locations, tips, strategies and videos on how to defeat the Black Knife Assassins easily, as well as boss stats and lore for the Black Knife Assassins."
https://eldenring.wiki.fextralife.com/Black+Knife+Assassin

Concealing Veil
"Concealing Veil is a Talisman in Elden Ring. Concealing Veil conceals wearer while crouching away from foes. Players can use talismans in Elden Ring to boost a variety of Stats."
https://eldenring.wiki.fextralife.com/Concealing+Veil

Sage's Cave
"Sage's Cave is a Location in Elden Ring. The Sage's Cave is found in Altus Plateau, west of Wyndham Ruins, under the cliffs. The cave's entrance can easily be reached by heading northeast from the Abandoned Coffin site of grace, past a large cluster of Poison Flowers."
https://eldenring.wiki.fextralife.com/Sage's+Cave