Feste disguises himself as a learned priest, Sir Topas, and adopts a different voice
Feste taunts the imprisoned Malvolio in front of Maria and ST, trying to make Malvolio truly believe he is mad
ST wants to end the joke with Malvolio as he is falling out of favour with Olivia, and leaves with Maria, Feste returns in his own guise as a fool and continues to torment Malvolio
Malvolio asks Feste for a pen and paper to write to Olivia about his treatment, Feste promises to return and departs singing and jesting
This scene shows the latent cruelty in comedy and offers a darker perspective on Feste's role
While other characters progress beyond their self-delusions towards love of another, Malvolio goes the opposite way as his vanity leads him from his self-confinement in yellow-stockings and cross-garters, where he is a literal laughing stock, to his imprisonment