I made this project by experimenting with Ask and Text to Speech blocks. At the beginning, when it says "Scratch Cat, Giga, Gobo, Nano, Pico, or Tera?" answer the name of the scratch mascot you want. If you answer anything else it will say Error and you will have to start the project over. After you've chosen a scratch mascot you can make them say whatever you want. Each one will have a different voice.
Note: If you choose the Scratch Cat sprite it will talk only in meows because it's a cat (I'm not joking it really does). All coding by me.