Which opera has more parts including acts and tableaux, Le roi d'Ys or Stiffelio?
Stiffelio Stiffelio is an opera in three acts by Giuseppe Verdi, from an Italian libretto by Francesco Maria Piave. The origin of this was the novel “Le pasteur d’hommes”, by Émile Souvestre, which was published in 1838. This was adapted into the French play "Le pasteur, ou L'évangile et le foyer" by Émile Souvestre and Eugène Bourgeois. That was in turn translated into Italian by Gaetano Vestri as "Stifellius"; this formed the basis of Piave's libretto.
Poro (opera) Poro, re dell'Indie ("Porus, King of the Pakistani region", HWV 28) is an opera seria in three acts by George Frideric Handel. The Italian-language libretto was adapted from "Alessandro nell'Indie" by Metastasio, and based on Alexander the Great's encounter with King Porus in 326 BC. The libretto had already been set to music by Leonardo Vinci in 1729 and by Antonio Vivaldi among others and was used as the text for more than sixty operas throughout the 18th century.