Algirdas Matonis recently shared what he called, 'The Most INSANE HARD' euphonium solo, "The King's Gambit" arr. by Anneke Kamerman. I think he may be correct. He played this with piano some time ago but this one is arranged for brass band. It spans five octaves playing the 8va/8vb options with lots of multi-tonguing and 2-3 fingerings. Sheesh!
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YouTube: https://bit.ly/3yvEOc5
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