-Spiegel, spiegel, wer ist der schön am meisten? -Du bist der schön am meisten -Danke, Spiegel
Not to be a smartass, but to complete your advanced education in telling fairy tales:
"Spieglein, Spieglein an der Wand, wer ist die Schönste im ganzen Land?" :)
(ein Spieglein = a little mirror)
I feel that this is a very obscure sentence that could have been made by: a moron, a robot, a comedian, a narcissist, a zombie, an etc.
Good question. Danke remains the same because it's "Ich danke= I thank ...". You're right that Spiegel is both singular and plural, but danken takes a dative raticle as shown by the very formal "ich danke Ihnen" (Ihnen is dative for Sie) And so the Dative Plural of Speigel has an n at the end like almost all nouns do. Therefore it would be Danke, Spiegeln