Changelings, Doppelgangers, and Shapeshifters. Many Fantasy and Sci-Fi universes have some species that can change their appearance at will (including Star Wars and to some degree Harry Potter), and in Tabletop games, species such as these seem like they could be commonplace. Anyone that prefers to play roguish characters has probably taken a look at these races in games like Pathfinder or Dungeons and Dragons. These characters seem fun, but in my experience, it’s only fun for the one playing the Changeling and is usually a detriment to fun to all other players.
For Game Masters that like to give your players the most amount of freedom in character creation, you may even be tempted to let these species exist. Even though there are some players that wouldn’t take advantage of these powers, there are two major problems that can come from a player being able to change their appearance at will:
1. Changelings destroy Social Encounters
Characters that would be non-Magical (or not extremely high tech) would have to use a regular Disguise skill with a Disguise kit in order to try to fool the opponent in a social encounter. In this case, the minimum amount of time to create such a disguise would be 10 minutes. In situations where the PC’s are sneaking, this isn’t so easily done. Furthermore, there is only so much that even the most clever disguise would be able to change, or a costume able to hide.
A magical character would have an easier time using an illusion spell to disguise themselves, or any character could use a magical item such as a Hat of Disguise. Magical disguises have the advantage of being much more versatile in terms of how much can change and how quickly it could be accomplished. However, in many cases, they have a time limit as well as other drawbacks. Scrying magic is usually able to see through illusion spells easily, and it stands to reason that any decent guard would have at least some training in determining when they are faced with an illusion, probably relying on sound, smell, and if the illusions do not react to the environment quite correctly. (I think lower level illusions would look like early CGI, with feet that slightly slide on the ground, the possibility of some objects going through other objects.)
And here’s where Changelings destroy the difficulty scale. Changelings are able to change their actual, physical, appearance, in less time than it takes to create an illusion based disguise. They would also be much better than disguise kits since they would not need to use prosthetics, as well as much better than illusions since they would not have the inherent weakness to Scrying rituals, or have inconsistencies related with illusionary disguises. In short, they do a better job, faster, with no downsides.
2. Changelings hate party dynamics
According to the Lore of Eberron (and other worlds seem to follow in this pattern), Changelings are persecuted by other races. Usually seen as being untrustworthy, thieves, con-artists, and tricksters, all Changelings would be reserved trying to hide their race from everyone they can. In this case, there is an In Lore Reason to hide the fact that they are a changeling. This would also hold twice as true if the player wished to become a thief, assassin, con-artist, or was already on the run. In these cases, a player character Changeling would have no likelihood to ever tell any character, including anyone within the party, that they were indeed a Changeling, no matter how much he grew to “Trust” them.
From the outside, this can be seen as an interesting development, one player hiding an aspect of their character until the other characters discover his secret. Secrets like this can usually create some intrigue, possibly some party drama, and as a whole provide at least one character with an opportunity for personal growth, but in the case of Changelings it will always come off as irritating at best.
The inherently “non-fun” part comes from the fact of how game-breaking the power of Changelings is in social situations. Players that have a Changeling character have a tendency to try to resolve social problems on their own, usually trying to circumvent other players to keep their motives and abilities secret. Over time this usually results in all social interactions turning into “The Changeling Show”. Other characters become less interested in social puzzles and problems, because either the changeling resolves it before they have the knowledge of the problem, or they let the Changeling resolve the issue because they have the best chance of fixing it.
3. Changeling NPC’s are a Cop out
Using Doppelgangers as reoccurring bad guys or as plot twists also take the fun out of the story for the player. Their natural abilities make them simply Too Good.
Even if the Big Bad was a Shapeshifter, and frequently showed up in various disguises, there would be no way the characters would know, or a Game Master would have to awkwardly ask for perception checks at strange times. When a player’s character finally realizes that the Evil guy that they were chasing was secretly the owner of the dry cleaner the adventuring party goes to as well as their personal ship captain, the player is likely to already be bored of the concept (Assuming they figured out the Changeling)
In the event that the player is surprised, the shock will be cheap. The goal of RPG’s is always the journey, not the reveal, so revealing that Changeling NPC’s can change form usually feels without value. Similar to a “Long-lost twin” or Clone that would be used in a soap opera. The most interesting way to use a Changeling as an NPC is for the players to Never know they were a changeling. It inherently defeats the purpose.
Moving forward with Shapeshifters
This is of course for the way that shapeshifter exist in these games and stories now. These tropes can exist in books and movies, and some can even be done successfully, but in RPG games they are doomed to fail. That is until we fix them.