that depends on just how magic dependant you want your army to be. the plaque of dominion is always a nice choice, but I usually choose the one that gives a 5+ ward save to the entire unit, I can't rememebr its name.
obviously you can upgrade its generation, I would always take 4th gen or better. the miscast ability is very nice when you are rolling that many dice at once
other than that, I don't usually take anything else. I might have the diadem of power, but more likely I will have enough power dice to wreck without needing to save any.
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