Disease Cloud for snap aggro, if someone steals aggro...Disease Cloud again.
If you're still struggling, the rogue needs to learn to evade, the wizard needs to tone it down, and the monk probably has OP Velious weapons or something.
The point being, a 2nd disease cloud at 50% mob health should seal the deal for mobs at your level. Save shadow vortex later for pre-aggro building on the next mob while it's mezzed, the enchanter will thank you
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Also also, keep taunt handy if you have fast pulls/clears. It can help sometimes and its mana free.