Transformation is the ability for an individual to alter their physical body into one specific form. The power is not to be confused with Shape-Shifting, which is the ability of an individual to alter his or her body into a variety of forms and shapes. It is also not to be confused with Molecular Reconstruction, which enables a person to alter the physical structure of other items or beings.
Traditionally, the origins of the Transformation power has its roots in either science or mysticism. In most cases, the effect lasts for a limited duration before the individual resumes their most common form. In some instances however, the transformation can become permanent. For example, when 19th century miser Cyrus Gold was murdered, he rose from the dead and took the name Solomon Grundy. As Grundy, Gold was transformed into a hulking ash-skinned brute of a being and has retained some semblance of this form ever since.
In most cases, the ability to transform from one state to the next is practically instantaneous requiring only a few seconds for the cycle to complete itself. One of the rare exceptions to this permutation is the villain known as Killer Croc. Croc was the victim of a mutation that initially gave him slightly reptilian features. Over the span of several years, Croc's appearance has become more akin to that of his namesake, and the effect is irreversible.
Other circumstances may require external resources in order to affect a successful transformation. In the case of Firestorm, two people (traditionally) must participate in the change in order for the change to take effect. In other instances, sometimes invoking the name of a higher power, such as "Shazam" is sufficient to prompt the change.
Several supernatural species possess the power of Transformation including Vampires and Werewolves. Vampires in fact, possess both Transformation and Shape-Shifting. Their Shape-Shifting allows them to assume the guise of either a wolf, a bat, or in some cases, a fine mist. Transformation enables a vampire to alternate back and forth between their human appearance and their more vampiric mien. Vampires commonly assume a form similar to what they looked prior to becoming a vampire. Through an act of will (or as an involuntary reaction from hunger), vampires can alter their physical features whereupon they possess more monstrous traits, such as a pale complexion, fangs, bloodshot eyes, clawed fingers, etc. Werewolves on the other hand, do not possess shape-shifting in the strictest sense, and can usually only alternate between their human form and their canine form. Some werewolves may have the ability to assume a form that lies somewhere in between human and wolf, but this is not a common occurrence.