The ender dragon (or trigon since it's a modded one) of ftb skies doesn't seem to spawn : the end have been reseted 3 times, but everytime it get reseted no dragon spawn. At first I thought I was just too late and he already got killed by someone else, but the end crystal weren't broken, and no bedrock portal spawned (the one to return to our base and the one to go to the place with end city). Both of them should have spawned when he got killed, and since there are no portal we can't respawn him using end crystal. Since it happened 3 times, I think it's safe to say that he doesn't spawn at all, and that it's not just a one time bug
We've tweaked the script a bit and believe we have fixed this. Let us know if there are any further issues.