The DT mechanism is the key
When the Guardian spawns, and begins his slow pathing around the room, he makes a -20% check to the boss' HP level. When he completes his path around the room and arrives back at his original spot, he checks to see if the boss current HP = the previous HP - 20%.
In other words, if he spawns at 100%, and begins his journey, the first check the Guardial will make, is to see if the boss is at 80%.
If bosshp = less than 80%, no DTs.
If bosshp= 80% or more, your raid will take four random death touches until you fix the HP.
If bosshp = less than 80% BUT regens to over 80%, your raid will take four random death touches until you fix the HP.
In addition, boss spawns three kinds of adds.
Fire = no mez
Earth = mez
Ice = mez but most resistant of all.
Have fun!