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[edit] Beating a Demi-Lich

To beat a Demi-Lich, you need to either get a mage or a Barbarian with +5 Weapons, then use the Barbarian's rage or have the mage cast immunity to abjuration then go in and slaughter it because that will make you immune to his Imprison spell.

[edit] The Staff of the Magi

The Staff of the Magi is probably the most powerful staff in the game, but you probably need to be on chapter 6 to get it. You can get it by having a Rogue Stone and going to the door right of the temple of Waukeen, there will be a door to the left of it which is trapped. Don't take that one, take the one to the south of it, you will be teleported to a weird plane, a lich asks you how you got there then for finding the place you must die, prepare for a battle with two powerful spellcasters and a Beholder and a few more enemies, the Lich is carrying The Staff of The Magi and to get out, you put the Beholder's Eyestalk in the pot to the right. It counts as a +5 Weapon, makes you Protected from Evil (invisible) and increaces your AC