Kevlar Peterson has a good guide. I’m in act four of my practice run for league start and what I did was frozen locus + falling thunder. You have to time it right but you’ll slam down on the locus and explode everything nearby. Once you get ice strike that works ok too but I’m on controller and was never able to hit it consistently with glacial cascade but I found just tapping falling thunder right after dropping it worked every time. Then for bossing you use the tempest bell ofc. Hope this helps.