From Blood on the Clocktower Wiki
Once you are familiar with the characters from the three editions in the core set, you may want to create your own unique character lists. These are called scripts.
Do you have favorite characters that you like to put in nearly every game? Have you thought of character combinations that would make for interesting and challenging situations?
At https://script.bloodontheclocktower.com, you can create a script from any combination of characters you own. This tool will also generate a night sheet for a game with your custom character list, making it easy to run.
Comparing scripts is a fun and challenging way to improve your designs. It is often a good idea to start with just a few core characters that you want to include, and build from there. Online at bloodontheclocktower.com, or on your local Facebook or Meetup group, there should be a community active in comparing their creations. You are welcome to join.
Adding Travellers to a custom game is easy. Just do so normally. Some Travellers may not be appropriate to mix with the characters in play, some will be. You can decide on five Travellers that merge well with your script before the game begins, or make a decision in the moment.
Some Fabled characters are designed to help you create unique and interesting games. Creating your own script is an art, and it may take a few tries to find something you are happy with. Luckily, you already have some Fabled characters to help you make your game run smoothly. Maybe you have an overabundance of evil in the game? Or only a dozen characters?
Fabled characters can also ensure your game has an unknown number of Outsiders (which allows players to safely bluff as them), or add extra misinformation when needed, or resolve situations where character abilities clash.
Handling strange character interactions is more art than science. When you create your own scripts, you’ll end up with some odd situations indeed. Maybe you’ll have an evil Saint? Or end up with two Philosophers wanting to turn into the same character at the same time? With over two hundred characters in the works, some weird situations will arise. While the Clocktower rules are written with this in mind, you might be uncertain sometimes about how two characters combine. Use your best guess. As the Storyteller, your decision is final—but make sure you tell the players that you’re making a ruling. It might not be the best call, but at least it will be a clear one.