CLASSICAL MUSIC REFERENCES:
0:00 Bach - Toccatta and Fugue in D minor (Opening)
0:24 Also Bach Toccatta and Fugue in D minor, specifically the start of the fugue section, is looped in the background of Bach's verse
0:29 If you didn't notice "B2TSM" is an acronym for their names Bach, Beethoven, Tchaikovsky, Shostakovich and Mozart.
0:42 "that's how you get the Art of Fugue" refers to a set of 14 fugues and 4 canons by Bach that are all based on a single theme, and ordered in increasing complexity. It's viewed as like a textbook of contrapuntal techniques.
0:50 The background loop of Mozart's verse is Symphony no.40 in G minor movement 1. Interestingly, Beethoven took inspiration from this symphony for his own 5th Symphony even copying out some bars of Mozart in his sketchbooks for it. No idea if this was intentional by TSV.
0:56 "attend my greatest mass" probably refers to Mozart's Great Mass in C minor. It's incomplete for unknown reasons. It could also refer to Mozart's Requiem Mass in D minor, which is probably his most famous mass. It's incomplete for known reasons; namely, he died while writing it.
0:57 "let me blow my Magic Flute" refers to one of Mozart's most popular and influential operas, The Magic Flute
1:02 "when you play my Nachtmusik" refers to Mozart's famous Eine Kleine Nachtmusik.
1:03 Tchaikovsky's verse takes its melody from the main theme of his ballet Swan Lake, most famously heard in the Act 1 finale.
1:11 "Gone is my Juliet" is a reference to Tchaikovsky's Fantasy Overture for Romeo and Juliet. It may also refer to the heartbreak in his life, however TSV may have overlooked the fact that Tchaikovsky was homosexual and so would be missing his "Romeo" instead.
1:17 Duh Duh Duh Dum refers to the opening and central motif of Beethoven's 5th symphony, sometimes called 'the fate motif'.
1:28 the background sheet music is Bach's manuscript for his Ab major fugue from Book 2 of The Well-Tempered Klavier.
1:31 The background loop is Shostakovich's DSCH motif which he used in many of his works, probably most easily heard in his String Quartet No.8. DSCH was code for his name, since the motif D Eb C B in German letter names is D Es C H, and the German spelling of his name is Dmitri Schostakowitsch.
1:34 "Sick of writing for the Stalin government" refers to Shostakovich's bad relationship with Soviet authorities (including denunciations of him, and the killing & imprisonment of some friends and family), while the Soviet propaganda department loved commissioning him to write patriotic music (e.g his 2nd Symphony) as he was a talented composer.
1:44 "Hear my last premiere" probably refers to Tchaikovsky's final premiere of his 6th Symphony, 9 days before his death. Some speculate the symphony was a suicide note.
1:58 In addition to Beethoven's 5th, the fugue section from Bach's Toccatta and Fugue in D minor pops up again in the background loop. Also the choreography is the standard conductor's signal for counting out a bar of 4/4 time (also appeared partially at 1:17).
2:12 The melody of Beethoven's verse is Fur Elise. Also, "Classical, Romantic got them both" refers to the fact that Beethoven's style is viewed as bridging the Classical and Romantic periods.
2:23 "Deaf to the hate" refers to the fact that Beethoven went deaf. People told him he couldn't compose when he was deaf, but he didn't listen to them. Most of his famous works came after he was partially or totally deaf.
2:29 The violinist is meant to be Paganini; the devil horns refer to him being so good at violin that he was rumoured to have sold his soul to the devil.
2:30 Sadly, I can't tie the violin solo to any specific Paganini work, but it resembles Paganini Caprice no.5, especially the run at 2:41
2:45 The song ends with the end of the 1st movement of Beethoven's 5th symphony
At 2:49 the pianist does not have the right sheet music music open for the end of Beethoven's 5th. Instead, it's a piano reduction of Tchaikovsky's Romeo and Juliet overture.