This is what happens happens when you (I mean, Dancer) use binary strings in 'Unicode context' (so to say). For example

perl -E 'my $m=q{ДДТ - Чёрно-белые танцы)}; binmode STDOUT, q{:encoding(utf-8)}; say $m'

There are plenty of ways to produce mojibake actually... Did you try something like

get '/np' => sub {
  return Encode::decode_utf8(`mpd | head -n1`);
}
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...just for testing? Anyway, this is probably a bug in Dancer.

For some reason, Dancer imports utf8 into your file

utf8->import; # line 232 of Dancer.pm
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Apparently, it expects Unicode strings from you. And `mpc|head -n1` produces bytes. The bad thing with Perl is that by default, it tries to decode binary strings from Latin-1.