After the zone change, Fellspine spawns all over the place. I saw him up on track from the CS zone, thought it was odd and followed tracking through the first tunnel on the right. I killed a few roamers on my way there and saw fellspine was fairly close. After killing him and getting his belt, I went after a rampaging bulthulk i saw on track. A few minutes later I saw Fellspine on track again! Turns out one of the first roamers I killed was a PH for him too. Got another belt (after transfering the first one to a twink) and a seahorse hide cloak.
Fellspine hits harder now, summons, and seems to have less HPs.