Lead with Piercing Strike to gain aggro followed up with your buffs (Great Fury/High Focus) and then Cleaving Roar. Pop Redemptive Barrier and transition into Thunder Blessing (to stack Cleaving Roar through Spectrum of Agony, and to become immortal during Redemptive Barrier). Cancel Thunder Blessing at the last second into another Piercing Strike and Shield Throw into a fully charged Fire Bomb (to make use of Shield Throw's 2 second heavy attack buff) followed by your skill choice of either Annihilating Slash (more AoE damage, gets bonus damage from Piercing Strike's weakness) or Ice Spear (more single-target damage, builds even more Cleaving Roar stacks). Follow this with Frost Smokescreen to keep Cleaving Roar going for longer and finish with Judgement Lightning (which will jump to multiple targets because of Frost Smokescreen). Your Cleaving Roar is now back up again. Use your Frost Smokescreen first because it has a cast time and follow it with Cleaving Roar to start stacking the debuff again.
Use shield charge when needed. Pop Redemptive Barrier liberally, otherwise save it for tank busters. Keep Cleaving Roar debuff up on multiple enemies with Frost Smokescreen and Thunder Blessing. Stack your party-wide buffs together. Go ham with Fire Bomb and Annihilating Slash when you can.
Despite the fact that this is a "mage" build, you actually want to prioritize all other stats over Wisdom. This is because using Thunder Blessing for almost its entire duration is part of the rotation, meaning even if you dip low (which you never should because SnS's mana costs are very low), you'll be completely refilled every minute.
You can tank SO MUCH with Redemptive Barrier on this build. Don't be afraid to pop it to soak massive tank busters and then refill with Thunder Blessing. I can soak all 3 tank busters on Temple of Slaughter without dipping below half health using this strat. You basically get two healthbars.
Enjoy!
