The reanimation of the deceased, recent or not, should not be taken lightly. Not all necromancy involves hate and evil, some like revivify are considered good and helpful by the public. One should note, the mundane and spiritual costs for reanimation are high, and intent affects everything in these rituals. To much emotion one way or the other can create a creature consumed with hate, every action inspired by the constant pain they feel. A calm-mind, and plans well considered, is arguably the most important ingredient when reanimating the dead.
A soul is necessary, and the original soul is preferred to lessen pain. Of course, other ingredients may be listed depending on the ritual and how long the subject has been deceased. A body is of course, necessary, and one should take caution here. Reanimating any state of the deceased is possible, regardless of state of decay, age, or other factors. But the most useful bodies are those that are unaffected by abnormalities, age, or length of time after death. A skeleton can sometimes be better than a mangled corpse, or mutilated body.
On the subject of freshness, careful consideration must be done. Have you ever wondered why so many skeletons in a necromancer's army? And even fewer zombies? And even fewer useful undead servants? The longer the body the remains deceased, the less control the original soul has over its body, and the easier it is to use a foreign soul. A spirit can stay tied to its remains for days, weeks, months, years, or even eons.
A wise necromancer will not wish to fight the spirit's emotions when creating his undead, finding it easier to coax the soul back into the body.
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