Okay, probably answered previously, but could not quickly locate.  Created my second tank - Necro.  Learning the abilities.  Curious on the possibilities of the Colossus Ult if or in combination with the boss having the Brittle debuff (minor or Major).  But I am still a little unsure of how to create the debuff in the first place.  Will obviously/likely have frost staff on back bar, wall, etc but what sequence or casts do I initiate to apply either debuff onto the target?
I presume that Major Vuln/Saxh(Major Force)/Brittle would be a good situation to have on the target.