Dreamrider is bad against beasts, and when they come from 4 sides at once you can't make the forgemaster surviving.
Btw: when the countdown for the respawn is over then they immediately run up when they are popped, and the abbyals will run up too (after something like 10 mins).
But i suggest, you recall on forgemaster, stuck dreamrider on backside (+ pull all monks and mesmers from behind forge (the 4 monks will keep them alive)) and then you kill frontside with the 2 mes and 2 monk from fromtide as aggro.
Another way could be, to spawn the beasts on front side, then pull them to forge entrance and then do backside with the 2 groups of mes/monks from backside.
I guess it's time for me to test this
