Mages are as in LL. PR is INT. d4 hit die, no armor. Mages get -2 to their saves against Paralysis, Breath, and Death (see Target 20). Mages always require a focus (amulet, wand, staff) to cast prepared spells; rings can be used as foci, but require one ring per spell. They must hold their focus to use it.
In addition to casting prepared spells per day as per LL, Mages can cast memorized spells at a cost of 1 HP per spell level. Mages may designate up to their INT in spells as memorized E.g. to cast a 2nd level spell would cost 2 HP. A Mage with 14 INT can mark up to 14 spells that she know well enough to cast without a book; memorizing a spell is semi-permanent, so Mages might not want to memorize as many spells as their INT allows at first level. Preparing a spell always requires a book (the procedure for putting the spell into the focus without expending XP is longer and more complicated). See Spell Casting
Mages must select a theme and stick to it. E.g. a Mage might be an ice mage, and all spell effects would be described in terms of ice (sleep might be encasing foes in ice, magic missile would be a dart of ice). If the spell doesn’t make any sense in terms of the chosen theme (e.g. a Floating Disk made of fire), then it’s not available to that style of Mage.