Simulacrum is a peculiar wizard spell that is widely held to be broken when it comes to power level, and is the source of so many rules questions that it is one of the very few spells has its own tag, simulacrum.
It has been part of the game going back all the way to 1st Edition. Simulacrum allows you to create a functional duplicate of a creature partly from their organic materials, and partly from ice and snow. (Depending on the edition of the game, other details differ; typically it has only half the hit points and cannot become more powerful from experience).
Does anyone know what the literary or other origin of the spell is, that would explain some of its unusual features?