Blood amalgamation is summoned by Nex in the Nex: Angel of Death fight when she reaches 2,100,000 life points.
It appears in the northwestern sector of the chamber. Upon spawning, player standing around it take 4000 typeless damage; this can be reduced via defensive abilities and other damage modifers. It has an adrenaline bar above itself that fills up over time. If the amalgamation is destroyed before the bar fills up, Cruor spawns with half his maximum life points - 150,000 - and a lowered combat level of 750. Otherwise, Cruor spawns with 300,000 life points and a combat level of 1000.