Under Mister Monday
Monday's Dusk was always loyal to the Architect, and triggered the events that caused Arthur to become the 'Rightful Heir To The Architect', including subtly releasing the Will. He has a black tongue, short jet black hair, black wings, and a black sword made from frozen moonlight.
Under Lord Arthur
Under Lord Arthur, Monday's Dusk is the previous Monday's Noon, as he was demoted after Lord Arthur claimed the First Key. After his demotion he spoke more softly, like the previous Monday's Dusk. He changed what he wore so he wore black, and his Commissionaire Sergeants swapped roles to become Midnight Visitors. He is now loyal to Arthur.