This is the 8402nd most frequent Russian word.
мэнсону
The word "мэнсону" is not standard in Russian, but it may refer to the name "Manson" in a specific grammatical case (dative or prepositional).
In this sentence, 'Мэнсону' is the dative form of a proper noun, indicating the indirect object to whom the song is dedicated.
Я слушал песню, посвящённую Мэнсону.
I listened to the song dedicated to Manson.
Here, 'Мэнсону' is again the dative form, used to show the recipient of the action (receiving the letter).
Мы отправили письмо Мэнсону в прошлом году.
We sent a letter to Manson last year.
'Мэнсону' serves as the dative subject of the verb 'предложено,' referring to the person being offered an opportunity.