This metapuzzle re-uses answers which are names of songs. When these songs are requested as indicated in the URL bar, a similarly named song from musical theater appears instead, the URL has changed, and the solver is asked what to play next. The new given URL is related by some mechanism to the song currently playing; apply that same mechanism to the next song in the musical (with playlists provided to guarantee a well defined order) yields a URL that redirects to a new song with a new URL. After several such links, the solver reaches a dead end with a new, mysterious URL. Each starting song produces its own chain and its own dead end URL:

Mary Poppins

Starts from BLACKBIRD -> Feed the birds.

Song	Given URL	Mechanism	Next song	Next URL
Feed the birds	mp-ftb	first letters	Supercalifragilisticexpialidocious	mp-s
Supercalifragilisticexpialidocious	1w34l	# words, # letters	Temper, Temper	2w12l
Temper, Temper	caughtyouatlast	what lyric first follows the title lyric?	Chim Chim Cher-ee (Rooftop Duet)	asweepisaslucky
Chim Chim Cher-ee (Rooftop Duet)	5v____eY____	(dead end)	(dead end)	(dead end)

The Great Gatsby

Starts from GREENLIGHT -> My green light.

Song	Given URL	Mechanism	Next song	Next URL
My green light	tgg-mgl	first letters	Shady	tgg-s
Shady	s-ninetimes	title first letters, then how many times title appears in lyrics	Better Hold Tight	bht-fivetimes
Better Hold Tight	bdeeghhilortttt	alphabetize title letters	Past is Catching Up to Me	aacceghiimnoppsstttu
Past is Catching Up to Me	_vv____Y7___	(dead end)	(dead end)	(dead end)

The Little Mermaid

Starts from SWEETCHILDOMINE -> Sweet child.

Song	Given URL	Mechanism	Next song	Next URL
Sweet child	tlm-sc	first letters	Poor Unfortunate Souls	tlm-pus
Poor Unfortunate Souls	ursula	who's the main singer?	Positoovity	scuttle
Positoovity	1w11l	# words, # letters	Beyond My Wildest Dreams	4w21l
Beyond My Wildest Dreams	__vE____70__	(dead end)	(dead end)	(dead end)

Fiddler on the Roof

Starts from IF I HAD A MILLION DOLLARS -> If I were a rich man.

Song	Given URL	Mechanism	Next song	Next URL
If I were a rich man	fotr-iiwarm	first letters	Sabbath Prayer	fotr-sp
Sabbath Prayer	aaabbehprrsty	alphabetize title letters	To Life	efilot
To Life	tl-nineteentimes	title first letters, then how many times title appears in lyrics	Miracle of Miracles	mom-fivetimes
Miracle of Miracles	___E3____0D_	(dead end)	(dead end)	(dead end)

Mamma Mia!

Starts from HONEY -> Honey, honey.

Song	Given URL	Mechanism	Next song	Next URL
Honey, honey	mm-hh	first letters	Money Money Money	mm-mmm
Money Money Money	mustbefunny	what lyric first follows the title lyric?	Mamma Mia!	hereigoagain
Mamma Mia!	papatio	take opposites of every word	Dancing Queen	singingking
Dancing Queen	____3N____Dd	(dead end)	(dead end)	(dead end)

Les Miserables

Starts from PURPLERAIN -> A Little Fall of Rain.

Song	Given URL	Mechanism	Next song	Next URL
A Little Fall of Rain	lm-alfor	first letters	Drink with Me	lm-dwm
Drink with Me	eatwithoutyou	take opposites of every word	Bring Him Home	takeheraway
Bring Him Home	valjean	who's the main singer?	Dog Eats Dog	thenardier
Dog Eats Dog	5____Ne____d	(dead end)	(dead end)	(dead end)

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The dead end URLs clearly fit together to make 5vvE3NeY70Dd. When this complete URL is requested, a final song clip appears, playing the short excerpt, "The demon barber of [blank] [blank]." The final answer is what goes in those blanks, FLEET STREET.