No your probably thinking of another game like Vacation or Abroad.
In Sims 2 Nightlife, there are only vampires.
Chat with our AI personalities
Indeed, Sims 2 mermaids.
There are no mermaids in any of the Sims games or expansion packs.
None of them have mermaids.
Sims 2 nightlife gets you the sim modder. I've just downloaded sims 2 nightlife and now I can get it, whereas I couldn't before ^^
To unlock cars on the Sims 2, you'll need Sims 2 Nightlife.