What actually bothers me even worse in this fight, are the people who grab the chain and hold it hostage til the last possible second. Getting free dps on the boss while it's incapacitated sounds fine on paper, but honestly, it only makes the fight longer. The belly phase amounts to 50% of Cerb's total HP. Holding the chain just delays how quick you get to that next belly phase, and damage done on the outside is negligible in comparison.

And, unless raid dps is just abysmal, and some unbelievable how, can't manage to do 25% damage before each belly phase ends, you'll usually end up killing that last belly phase somewhere around 15% with this method. Which of course, translates to a full 10% hp worth of instant damage, totally wasted.

So seriously, just put the chain on, and let's proceed with the fight.