As the action progresses, the downfall of the Theban dynasty proceeds culminating in the action of a maenad.  
In the first of three encounters with his cousin, the protagonist of this play turns into a bull and then a shadow.  That protagonist is disguised as a stranger from Lydia.  As the action progresses, the downfall of the Theban dynasty proceeds culminating in the action of a maenad.  At the end Cadmus appears, comforts his daughter, and mourns his grandson.  Of course his daughter, Agave, had just torn his grandson, Pentheus, to pieces.  FTP, identify this Euripides play centering on Dionysus and which takes its name from Dionysus' attendants.
In the first of three encounters with his cousin, the protagonist of this play turns into a bull and then a shadow.  
The Bacchae