Video includes healers speaking on vent and coordinating portals. (you can see them trying to pop the last cloud together)
More than one healer can benefit from one cloud explosion.
Valithria slowly looses health, so more healing is needed, end of the battle is especially important.
3 healers on 10 man, 7 or even 8 on 25 man.
2 healers go through portals on 10 man, 4 or 5 on 25 man (having too many healers going through the portals will cause some of them to loose the buff stacks if they don’t coordinate the last cloud)
Healers must not drop the buff stacks. (Hit a cloud just before dream time ends)
Cleanse Gutspray on tank.