Lancer is the Part 2 / Pop culture of the delusional and earnest seeking of idealism, and hinted in his bond with some of his final hours of lucidity before he died, the Berserker is how Cervantes intended him to come off in Part 1 as a complete and utter deranged selfish lunatic.
His Noble Phantasm is basically a reality marble, akin to UBW or Nameless Forest, but much, much more fragile thus partly why gameplay wise he's stunned after using it.
yeah, really Part 1 is a Satire on Chivarlic romances and overt idealism while Part 2 also went and "Hey you know, the Cynical jerks aren't right either,"
Echo
and also degree of self-awareness, Lancer is still mostly delusional, but he has his moments of lucidity that he's an old man with a huge wellspring of belief and desire before going back to Knight-Errant
Also why is he speaking in Ye olde english? He speaks a form of Castilian that was outdated in 15th century spain, Early Modern English is the closest equivalent
like ngl, the physical description is the hard part as I want key points without just - doing the same thing every person who did a description/appearance for Quixote did.
also because Cervantes was probably tired of writing it out when he wrote part 2 as he drops it there