They may sing nice, but they like raising mice and rats as mounts.
And this is bad because...?
Ah but this would never work for I know their weaknessesFor you it's bad because they might try to enslave you.
For me, it's because I don't like most rodents, specially ones named Mickey.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.