I found it a little harder to get this by straight smash and grab. I had to go in the backway through the secret tunnel. From there i pulled the 2 golems and roamers that came near alter. After that i cleared the (facing alter from secret tunnel) right side and the middle. I single pulled the one closest to the skull on the left. After that said the words and bam! he spawn. The only thing i did different is i pulled him into the tunnel and fought him there. If not, i tended to get adds and had to gate out.