A song starts in sunshine, but has a dark reprise.
There are two main forms; the first is the sarcastic echo, the second is the dark reprise. This trope is favoured by the writers of musicals.
The sarcastic echo is a duet, but one party is oblivious to this fact. The main singer opens with a happy, even sappy verse. But there is an onlooking character mocking the first from the wings.
The other [...] [tvtropes.org]