On our last nights kill we did the following:
Raid comp was two tanks two healers (rdruid and rshaman) and mixed dps.
P1:We kept releasing people ASAP , no puddles were consumed. Had one ranged dps on slimes trough out entire P1+P2 so we made sure they are dying one by one before next set spawns.
P2: Again we were releasing people ASAP , no puddles were used. IF controlled person had it's CD ready on Amber Strike we were interrupting Monstrosity's explosion , otherwise I just called for some Raid CD's to reduce the dmg income. In all honesty , explosion from Monstrosity doesn't hurt that much , compared to explosion from construct.
If it goes trough there are high chances you will lose someone.
During this phase , if healer (s) get reshape life on them , we were saving personals , healthstones and were releasing him/them ASAP.
P3:Just before we've finished off Monstrosity we started to build up stacks on the boss via Amber strike , then we all stacked near the boss and rotated some raid CD's.
Interrupt yourselves > eat the puddles to regen energy if yer bellow 50% and zerg is pretty much what you gonna do.