The problem with dragons is that you only hear about when they get killed, thus leaving the impression that dragons are huge, fire-breathing, enormously destructive creatures that are really quite easy to take down. The difficulty lies not with unicorns themselves, but with airbrush artists. I'll limit myself to observing that with the increasing popularity of vampires, we're on the verge of the unicorn syndrome all over again. The most incredible power of mermaids, of course, is their ability to keep their hair covering their nipples at all times. Or, in the case of cartoon mermaids, the ability to wear seashells as a bra without bitching about the rough edges.
Manatees are among the least mermaidenly of all mammals.
It would be easier to mistake Al Gore for a lovely young fish-woman. More likely some sailor had a thing for manatees, and invented the mermaid-mistake story to keep the other sailors from ribbing him about it. It's said that ancient legends have lessons for humanity, even unto the present day. Aside from that, though, werewolves are pretty cool. You turn into a murderous, slavering wolf every full moon.