In my current game, I made a Grand Staff of Power with:
* +20 Spell Skill
* +3 to hit
* -4 Spell Save
* 4x Phantom Beast
It costs over 5,000 Crystals, but I gave to an Illusionist and now he can annihilate Elite units in a single shot. With a ring of Flying, Magic Immunity, and Invisibility, he can take out entire armies by himself without a single scratch. To add insult to injury, there's four Phantom Beasts in it, just as if it wasn't absurd enough.
I found or made 3x -4 spell save items and gave to a hero just to prove that it allowed him to cast 'drain power' with a huge enough resistance penalty that he could make undead great drakes. Not that it was overly useful, just did it for a bit of fun :)