If your character has a different sprite or sound for the mechanics then be sure to make a different sprite inside the project and also add a sound in the project as well if you have it so I can add it into a game. You can also have a mechanics that your characters can appear when the player enters a room or something like that as well and remember that this is not a scratch game. It's a Unity game. This characters will be added in the V1 of the game. Also make sure you tell if the difficulty is higher, what will they look like. Also the character mechanic that you gave it me must at least does something to the player like distraction, annoyance or even killable character.
C2A