SRD:Creature Spells and Powers
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Sometimes a creature can cast arcane or divine spells just as a member of a spellcasting class can (and can activate magic items accordingly). Such creatures are subject to the same spellcasting rules that characters are, except as follows.
A spellcasting creature that lacks hands or arms can provide any somatic component a spell might require by moving its body. Such a creature also does need material components for its spells. The creature can cast the spell by either touching the required component (but not if the component is in another creature’s possession) or having the required component on its person. Sometimes spellcasting creatures utilize the Eschew Materials feat to avoid fussing with noncostly components.
A spellcasting creature is not actually a member of a class unless its entry says so, and it does not gain any class abilities. A creature with access to cleric spells must prepare them in the normal manner and receives domain spells if noted, but it does not receive domain granted powers unless it has at least one level in the cleric class.
Creatures with psionic powers are similar to creatures with racial spellcasting ability. They have the ability to manifest powers just as a member of a psionic character class can (and can activate psionic items accordingly).
Creatures with the ability to use powers are subject to the same rules for manifesting powers that characters are, but they are not actually members of a class and do not gain any class abilities unless otherwise specified.
Creatures with psionic powers generally emulate the manifesting ability of a particular psionic class. When such a creature takes levels in that same class, it can stack its innate psionic powers and its class power progression together.
Creatures with psionic powers that take levels in a class other than the one they emulate combine their two power point reserves into a single reserve, but they manifest powers from each psionic class separately.