The Sisters of Parvos update in Warframe saw many systems added to the game, or expanded and changed. The Kuva Lich system saw some important changes, and the Sister of Parvos system that was added brings even more enemies to deal with, and rewards to earn.
An important and interesting system for both of them is the new Requiem Ultimatum. The Requiem Ultimate is a new item that can drop when you vanquish your Kuva Lich or Sister of Parvos. It is quite rare, as both enemies are tough to deal with and can only be killed over an extended period of gameplay and time in the game.
The Requiem Ultimatum has a 25% chance to drop when you Convert of Vanquish your Kuva Lich or Sister of Parvos, and it will only drop for the person who “owns” the relevant enemy, so you cannot pick up Requiem Ulimatums for other players.
The player can then use the Requiem Ultimatum to force their Kuva Lich or Sister to spawn in a mission, as long as the mission is taking place on an influence node. It is a useful way to increase the speed of hunting the enemies in question, and farming their weapons and drops.