Shapeshifting is a common motif, all the way from Greco-Roman myths to Harry Potter. But before you introduce shapeshifting magic into your campaign, here's eighteen questions you may want to ask yourself.

1. Can you change fingerprints and retina scans?

Say Eve polymorphs to Bob, and is trying to convince Alice to hand over that wallet/password/key. How does Alice know that Bob is actually Bob? A-ha. Alice happens to have a fingerprint kit. She takes Bob/Eve's drinking glass and goes CSI over it. What does Alice's fingerprint exam show? Does it matter if Eve had a copy of Bob's fingerprints already?

Teleportation often has the requirement of "know where you're going." With illusions, it is literally "what you see is what you get." Shapechanging is different, because you really can't know everything about a subject before you change to him/her/it. So, is shapechanging nothing more than a tactile, very good illusion?

2. Can you change DNA?

Again, we have Eve and Alice, but instead of a single fingerprint, Alice has a super-sophisticated crime lab that can do DNA testing. Alice takes Bob/Eve's drinking glass, gets some saliva, and does a full DNA scan. Again, what happens? If the DNA doesn't match (and if the answer to #1 was no, if Eve couldn't copy something as single as a fingerprint, then DNA is right out of the question), then how can a player shapechange into a flying monster and actually fly, or change into an ogre and have the strength of an ogre. Complications, complications.

3. Can you change brainwaves?

Assuming that Eve has the same physical neural framework as Bob, would a scan reveal any inconsistencies? If not, then that opens up a few more doors. If Bob is autistic, then there's the possibility that Eve also becomes autistic; studies are inconclusive, but there may be a physical component to autism. The AD&D and GURPS rule of thumb is "physical things go with the body, mental things go with the mind." It works, but intelligence is somewhat physical as well.

4. Does your handwriting and "motor skills" change?

Building on the "mental things go with the mind" paradigm, say Bob is a professional violinist. Eve shapechanges. Can Eve play the violin? True, there's a lot of mental ability, but how much of the skill is physical ability and muscle memory? Reverse the question -- if Eve is the concert violinist, can she play in Bob's body? Anyone who's played and then put away an instrument knows that half of practice is building the muscles and callouses to quickly hit the notes. How about singing? What if Eve or Bob is one of those savants, who have artistic ability with no training? I can picture, if you excuse the pun, people shapechanging to a savant just to get artistic talent, paint something, then change back.

5. Can you change from being right-handed to left-handed?

Say Bob is left-handed. Eve is right-handed. Eve changes to Bob. Is Eve confused, because her dominant hand is suddenly weaker and less dexterous? Or does Bob's muscle memory take over?

6. Can you shapechange your soul?

Metaphysical question here. If you can't change your aura, then do you get the alignment of the subject you change to? This makes shapechanging much less desirable. Yes, you can change to a black dragon, but you become evil. Or do you have to fight urges to become evil, which makes for fun roleplaying (although no one likes to hear a monologue). If the soul doesn't change, then soul readers can be used to detect people, devaluing fingerprints and retina scans.

7. How do you tell people apart?

A more practical question. Alice is staring over wine at Bob, or who she thinks as Bob. She has a suspicion that that's not Bob. What to do? Depending on the above questions, it may be moot, but what if Eve is a perfect copy of Bob?

The obvious idea is a password, passphrase, or shared memory. It's basically a trope. "Bob, do you remember where we went on our first date?" and Bob better answer "we went to a country-western bar at New Year's Eve and had a horrible time" or Alice knows something is up. And that works fine for intimate partners, but what if Alice and Bob just met? They can agree on a passphrase, of course, but that requires work and forethought.

Another option is to have equipment do the validation. RFID devices can be swallowed or implanted, and theoretically they would not be "polymorphable" because they're not part of that person, any more than a cyborg can be copied whole. Of course, if artificial items can't be added, then make sure the subject you change to doesn't have a pacemaker.

8. Can you heal yourself or cure diseases?

If damage and disease are just another form, then why keep it? If you're changing back to yourself, you might as well change back to a perfect copy of yourself, not one besot by damage. The real reason is "game balance." It makes shapeshifting incredibly powerful if you can heal yourself.

9. Do you age?

Yeah, if instant health isn't enough of a draw, why not shapechange into someone just like you, just at the prime of your life? GURPS Transhuman Space talks about the issues of people essentially living forever. The good: people plan for the future, skills don't go away. The bad: power tends to collect into a few people, and they never give it up.

10. Do you remember your original form?

Back to the soul. The cliche is "don't get sucked into what you turn into," but this makes sense if you turn into something with an animal intelligence. The mental capacity just isn't there. Spells may be set in advance to only last an hour, long enough to do what he needs to do, and then force the spellcaster to change back. Then again, can you change back? Do you know how much you weight, what your height is, what your fingerprints are? If a shapechange spell wipes your body, can you recreate it like pressing an undo key? Or are you building your body from scratch?

11. How does your outlook on life change?

I'm reminded of The Shapechanger's Wife, a wonderful book by Sharon Shinn. I can't paraphrase it or even quote from it because all my books are in boxes (got to love moving), but just find it and pick it up. The main wizard can change his and other's shapes, and creates a wife, well, I won't give it away. Let's just say that the wizard acts like a god, remaking people in the image he thinks they should be.

I'm also reminded of Eberron, where a group of changelings don't have a true form (the "becomers"); their true self is their mutability. They just change to whatever suits them, flowing with the current culture. A second group (the "reality seekers", and while the names are neat, they smack of "made up game term") tries to find their true self, changing from one thing to another to polish themselves into the best they can be. Two possible outlooks among many.

12. How do other people value life?

If you become a cow, know what it's like, can you eat beef? And, if your friend could turn into a cow, would you eat beef? Yeah, that particular steak isn't from your friend or another shape-changed human, but all it would take is one scare, one mixup, and suddenly a lot of folks get sick and turn vegetarian.

13. Does your charisma change?

AD&D combines Comeliness (physical beauty) and Charisma (personal magnetism) into one stat. Many other systems have advantages, perks, or whatever the game system calls it to represent physical beauty. But part of that magnetism is mental, and part of it is a combination of physical and mental; they move well, feel comfortable in their skin. Can a shapechanger feel comfortable in someone else's skin? Or would the idea that he can change into whatever he wants to add to his charisma, give him a sense of confidence that others don't have?

14. How do you gain or lose mass?

Change into an elephant. Where does the extra mass come from? One of the Wild Cards characters used energy to convert to mass, but that's a lot of energy; they handwaved that part away. Other ideas include some extradimensional portal that you borrowed mass from. It's magic, but following some rules of physics may help in the realism department.

15. Can you change to inanimate things?

If you can change into an elephant, how about a rock? Or a shrubbery? Or a diamond? Would you be indistinguishable from any other rock? If you were shattered, would you die? Rocks don't die, they just change shape. More complications.

16. If you can shapechange items, what happens to currency?

Part of the value of things are its scarcity, either because of natural limitations (how many diamonds are there) or cultural limitations (anyone can paint, but there's only one Mona Lisa). Forgery is an issue in the modern world; shapechanging makes it that much more difficult to combat. Nations have techniques to prevent forgery; magical tampering would have to be added to the list. And for some things, forgery isn't necessarily a bad thing. If I create a diamond to be an exact replica of the Hope Diamond, then everyone will decry it as a forgery. If I create just another flawless diamond, then is it a forgery? What if you create a Dell Computer?

17. How much do you need to know about the object before you shapeshift into it?

This is probably what I've been circling around with all these questions. You can't know everything about what you're shapechanging to. There's too much information. Most stories do a half-baked "you must know the soul of what you're changing into", or just dance around the idea. I have a concept of "a wolf" and have seen some in the wild, but I couldn't tell you how long the legs are suppose to be, or how bushy the tail is. Some of those details may matter. And that's just the physical aspects; I have no clue how a wolf's mind works.

The "need to know" can be a good game balance enforcer, but more often than not, it's too broad, making the power useless. But if you don't have some type of game balance, you end up giving the player a Swiss Knife of spells. Need to heal, just transform into something that's not broken. Need to fly, transform into something that flies.

18. What's the next column?

Wonderful question. We did tricks of the mind and tricks of the body. Next in the triad are tricks of the soul -- mind control, charm, and swapping bodies.