The correct answer is ironic tone.
Shakespearean tragedies obviously do not have cheerful endings given that they are tragedies - the endings are always bad and sad. Shakespearean comedies do not have a melancholy tone given that they are happy and delightful. Comedies also do not have characters who experience feelings of guilt - they mostly appear in tragedies. So what comedies and tragedies do have in common is ironic tone - the tone of mocking something or someone.