Simulacrum: A spell which creates the duplicate (form only) of any person the Magic-User desires to duplicate.It's a sort of golem, really, made out of snow. But what exactly does the spell do. It says it creates a form that duplicates another being. Given that other spells must be used to animate it, it's possible that it is literally just a non-mobile form. The later AD&D version of the spell specifies that it is essentially a zombie; that's probably a better approach than a truly immobile duplicate, because otherwise Polymorph Other might seem to be an easier way to accomplish the effect.
In order to make a complete Simulacrum several other spells are necessary. If snow is not available the user must cause an Ice Storm from which to fashion the form. When the form is completed he must then use a spell to Animate it.What spell is used to Animate the simulacrum, and what does that even mean? The only M-U animation spell listed is Animate Dead, which is plainly not was intended. Again, the AD&D version changes this to Reincarnate, and it suggests what "animation" means in this context: "A reincarnation spell must be used to give the duplicate a vital force". In other words, to make a simulacrum mildly self-controlled and not just a manually-controlled robot, it has to be invested with a soul.
Finally, a Limited Wish must be used to give the form a personality and knowledge similar to the real person which it imitates. In no event will the Simulacrum have the full-abilities (knowledge, level, etc.) of what it imitates, but it will range from 30% to 60% of them.This became a topic of debate in the forum thread. Someone interpreted the AD&D version of the spell as allowing the creation of any kind of monster, including dragons, complete with special abilities. This is probably based on too broad an interpretation of the AD&D wording, which says "a limited wish spell must be used to empower the duplicate with 40% to 65% (35% + 5% to 30%) of the knowledge and personality of the original". That "empower" suggests to some people that all "powers" are covered, although it's pretty clear it doesn't even include magic, only skill and personality. At best, a simulacrum of a wizard would be able to read a scroll or use a wand, but a simulacrum of a dragon, assuming that is possible, can't breath fire or casts spells.
Now, a simulacrum could be transformed from an ersatz red dragon into a real red dragon via the Polymorph Any Object spell. Assuming it's already been endowed with a soul (via Reincarnate,) the effect should be permanent, and the newly-created dragon would be able to breath fire regardless of whether a Limited Wish has been used. That would be a way to create your own monsters. The Greyhawk spell does not require a piece of the creature to be duplicated. Does this mean that a wizard could duplicate made-up creatures? Could this be a source of the monsters in the world?
It is possible to detect a Simulacrum with a Detect Magic spell, close association, and so forth. If the real person confronts the Simulacrum the real person will be easily identifiable. If, however, the real person is dead the Simulacrum will slowly gain the abilities of the former person (1%/week) until it reaches 90% similarity in all respects; beyond this it cannot go. At all times it remains the thing of its creator, and whatever its creator tells it to do it will comply.Unlike the AD&D version, the Greyhawk Simulacrum spell allows the simulacrum to improve beyond its starting limits if the original dies. This raises the question: can you skip the Limited Wish if you just kill the original, or does killing the original only work if the two are linked via the Limited Wish?