Shapeshifter

It is not hard to believe that with all the portals to other worlds opening up, sooner or later beings who can change their shape would be encountered. And there are enough of them that being a shapeshifter comes with its own status, rights, and difficulties.

Willing, conditional and unwilling shapeshifters

Depending on whether a shapeshifter is capable of transforming out of their own will or not, they are usually divided into 3 categories.
Willing shapeshifters are all shapeshifters that decide by themselves whenever their transformation occurs. They might be limited by the number of times they can go through it the duration of each change, or not be limited in any way, but still, they are the ones who "press the button" to transform in the first place.
Conditional shapeshifters transform only whenever certain conditions are met. For example, lycanthropes can only change under the light of the moon, and merfolk will change whenever they enter the body of water. The conditions vary a lot between each type of shapeshifter and depending on how easy is to meet them or how hard it is to avoid them, they can be very close to being a willing or unwilling shapeshifter.
Unwilling shapeshifters are the ones whose transformations occur at seemingly random intervals, without any input of the shapeshifter. Shapeshifting caused by curses is the most common kind that falls into this category, though there are some species of creatures that also go through this.

Types of shapeshifters

While it is good to know whether a shapeshifter can change by their own choice or not, the more important classification describes the type of changes they can go through. And depending on that, there are many different categories that need to constantly be updated and tend to change quite frequently, which some consider quite an irony. At least the ones who don't have to actually catalogue those changes and any changes to the laws related to each category.
Body changers are the shapeshifters who can only go through the change of their whole body at the same time. If they decide to mimic someone of another species, they will completely change into them.
Compared to Body changers, Chimeric shapeshifters can change only parts of their bodies. They can achieve the same results as Body changers, but it will require more focus out of them. They also need way more knowledge on the inner workings of the parts they decide to imitate, otherwise they will only copy their appearance, but not their function. Most of Chimeric shapeshifters can add or subtract the limbs to their bodies, but doing so tends to really strain their minds and their bodies with each added or subtracted limb.
Fixed shapeshifters can only switch between few appearances, usually determined by their status. Many of lycanthropes can be counted into this category, as they can only switch between two or more forms. The greatest benefit of being this kind of a shapeshifter is that they never have to put in more focus into changing themselves as the predetermined shape exists already.
Phase transiting - some of thee shapeshifters, instead of changing their form, can change the state of the matter their bodies consist of while retaining their body functions. Turning into liquids, gases, something ethereal, or spiritual, those all belong to this category. Many oozes and slimes belong to this category as well as some species of vampires (at least partially).
Shapeshifters known as Borrowers are the ones who cannot come up with a form they change into on their own, instead they can "borrow" one's whole body or only their parts. Said "borrowing" requires either an eye contact or a physical contact that lasts for the period of transformation. Similarly to the Fixed shapeshifters, this time of transforming requires lesser amounts of energy and concentration, as new parts already exist, just on someone else.

Shapeshifting and personality

All shapeshifters tend to be at least somewhat eccentric. Some can sometimes forget what form they are currently in, others can become almost addicted to the changes. Some treat their transformed bodies as other people, and some really switch their personalities, not always out of their own volition.

Shapeshifting and laws

While each world has its laws that can vary a lot, many of them have to come up with how to deal with the shapeshifters. In most civilized worlds, it is illegal to impersonate someone else by completely taking their form, pretending to be them, using their appearance to gain benefits one wouldn't experience without transforming into them.
Most of the governments require declaring one's ability to shapeshift before and after entering a new world and should they decide to stay in one of them, they need to fulfill the required paperwork and register officially as shapeshifters. Some governments might even monitor them and require periodic visits where they will be evaluated for how they used their powers or might even require installing or implanting a tracking device under the threat of prison or deportation from the world should a shapeshifter decline.