Help - T3 Unique maps - City of Urek

Hello so I have been playing SSF a bit with my assasin and a unique T3 map dorpped - City of Urek. What I can read there is supposed to be a "second boss" in the unique maps but I can't seem to find it.
I killed some guy and got a pillar on my map. It says on the map that he is guarranteed to drop a Unique. The boss i killed didn't which leads me to think I have missed something, Please help!