Some time later he was introduced to Girish Ghosh. The two developed a mutual respect; Mustafi joined in creating the National Theatre. On its inaugural night, 7 December 1872, he played four roles in Dinabandhu Mitra's Nildarpan or "Indigo Mirror". The four roles were the villainous Mr Wood, the zamindar Golak Basu, his wife Sabitri, and a cultivator respectively. His pantomimes like Mustafi sahibka pakka tamasha or "Mustafi Sahib's Pukka Entertainment" in 1873, Sharadiya pancharang or 'Autumnal Pantomime' in 1889, or Bhagaban bhut or "God Bedeviled" in 1905 were not mere fillers but often became die centre of attraction for audiences. Mustafi moved from one company to another throughout his life, leaving no stage untrodden. He acted in various theatres as for example Indian National Theatre during 1872-3, 1883-6, Great National during 1874-80, Emerald during 1887-8, 1889-92, 1894-6, Arya Natyasamaj in 1888, Minerva during 1893-4,1896-1902,1904-8, Aurora in 1902, Star during 1903-4, and finally Kohinoor in 1908.
Ardhendu Sekhar Mustafi was very fond of innovative things. He was reportedly mentioned as a great actor and specially a comedian. In the absence of sufficient documentary evidence he is remembered more as a teacher. He trained nearly all the major actors of later generations, including Binodini Dasi in her initial days. Mustafi was a champion of natural against stylized acting. He knew how to make even a minor character shine. He was equally brilliant in major roles. His interpretations immortalized Jaladhar in Mitra's Nabin tapaswini or "Young Hermitess", Raja Malhar Rao in Amritalal Basu's Hirakchurna or "Diamond Dust", Robert Clive in Nabin Sen's Palashirjuddha or 'Battle of Plassey. Some other prominent roles can be mentioned as Bhaktaprasad in Madhusudan Dutt's Buro shaliker ghare ron or "Mane on the Old Myna's Neck", Nimchand in Mitra's Sadhabar ekadashi or "Wife's Widowhood Fast", Ravana in Ghosh's Meghnadbadh or "Killing of Meghnad", the lead in Ghosh's Abu Hosain, Jogesh in Ghosh's Praphulla, Karunamay in Ghosh's Balidan or "Sacrifice". With all these roles he has done complete justice.
This legendary artist died in the year 1908.