Mimics

Mimics, also known as Lures, are anomalous enemies similar to Money Bags in nature that disguise as several objects, and in rare instances, can even disguise as other enemies and terrain or platforms. When Mimics turn into their non-disguised form, the actual design is inconsistent, though the most common form is a black slime-like creature with red eyes. It is not known why exactly this design was chosen before Mimics were presumably scrapped, with the model potentially being a placeholder or the strange design simply being due to the enemy's mechanic of transformation. Mimics have commonly been reported to be very glitchy and unstable, likely due to their abilities being somewhat difficult for the Personalization A.I. to reimplement.

Description
Mimics have been said to appear in any existing level and can take the form of any object or piece of geography in the base game, or even personalization-exclusive objects such as a Fire Flower, though certain objects such as enemies, Power Stars and map geography appear to be rarer than simpler objects such as coins, potentially due to the Personalization A.I.'s failure to restore those properties of the enemy, or the Personalization A.I. giving the Mimics the ability to transform into more things based off of it's mechanic in certain cartridges.

Mimics can supposedly be revealed by going close to them if they are an object like a Power Star or coin, or ground pounding or punching the object they transformed into if they take the form of a platform or piece of map geography. Mimics can either instantly disappear, run away from the player and potentially transform back into their disguised form in a similar manner to Money Bags, or begin attacking the player through varied means. Mimics can reportedly defeated through all potential attacks, or can be invincible in rarer instances, which has been theorized to be caused by the Personalization A.I. failing to give the Mimic collision

Mimics have even been reported to appear as boss fights when they appear in Princess Peach's Castle or certain areas in levels that can function as boss fight arenas. When boss fights, Mimics have been reported to disguise as more valuable items or objects, such as keys or cap switches. Boss fight Mimics have also been said to be much larger than standard Mimics, especially if regular versions of Mimics appear in the same copy. A final property of boss Mimics is that they can supposedly transform into objects that can be used to attack the player, such as a Big Steely. If these boss fight Mimics are defeated, the most common reward is the object the Mimic was first disguised as, or simply a Power Star.

Theorizing
Mimics appear to be very similar to Money Bags in some regards, though much more generalized in what they can transform into, potentially implying that Mimics were the early versions of Money Bags before being removed for whatever reason. An alternative theory is that Mimics are created by the Personalization A.I. loosely based off of Money Bags, explaining why the most common design for Mimics are simplistic, why they can transform into almost anything in Super Mario 64, their occasional invincibility and other, more unstable aspects of the enemy.

Due to the ability of Mimics to transform into map geography in rare instances, it has been speculated that reports of map geography changes or additions to level maps were actually caused by Mimics due to the Personalization A.I.'s inability to edit level geometry without the use of some other anomaly such as Major Level Expansion.