I got a constant string of Wereass' in only my second ever embark, which only lasted about 8 (real) hours. They lived up to their name - asses. One would appear and kill 5-10 dwarves in a single hit each despite only being around for a day before turning into an Elf.
I thought that wasn't *too* terrible, even though, it being my second ever embark and only a few hours into my DF experience, I hadn't the slightest idea how to avoid them, let alone combat them. Until a couple of game months later when I realised that my dwarves were now infected, and they were now turning into asses from inside the fortress as well. I quit at that point, and did custom world gen for my third embark to turn off nearly all nasties until I understood the game better.
So, yeah. I've only done three embarks total and am still playing my third one, some 80 hours in (learning all the game mechanics before I eventually get around to restarting with more danger/Fun), but between those I've had Wereass', maybe 10 or 15 Titans, and Trolls and various other underground things from digging deep into the caverns. And that's with my embarking in Serene biomes with 95% of my play time in a fiddled world gen with 90% of the available beasts turned off.
I only started playing three weeks ago so all of this is on 40.24, and I hadn't exactly got the impression that there were only a few nasties out there..