Primal Bosses" are better known as "Forgotten Warriors in Redemptionrsps 317. It is a level 130 boss . Forgotten Warriors can be found in your Magic Spellbook - Boss Teleport - Forgotten Warrior.
In this server Forgotten Warriors aren't very hard to kill. But, it is recommended that you have a prayer level of at least 92, so you can pray "Soulsplit". You could also pray "Turmoil", which requires 95 prayer. You can kill the boss with almost any gear, you don't need any sort of special gear for it.
Since the Forgotten Warrior is a boss, it is included in the Soul System, converting all common and uncommon drops into souls. The Forgotten Warrior, along with all other NPC's in Redemptionrsps, drops the Infinity Key and immortal stone fragments