Lately hydras have basically been the number 1 cause of death in my monster island games. I almost miss the early DF2014 when literally any enemy would chicken out and run, even if they had the fearless token like hydras do. Made me feel like I was the all-destroying, all-devouring megabeast. owo
Also, as a highly belated response to earlier suggestions I just hacked zombies up. It works great. If you aren't outdoors in an evil biome, and not near a necromancer. In any conditions where the source of the undead horde is present and can't be eliminated first, the short-term benefits to incapacitating the undead has to be weighed against the long-term threat of multiple reanimated bodyparts.
Even the most harmless bits and pieces of zombies provide a few extra attacks aimed at you that can get lucky, a few more distractions to dispose of, and a few more additions to the swarm reducing your options to escape.
Though to me at least, the best defense against the undead is a good pair of feet. Just don't ask to borrow some from the zombies. o3o
EDIT: Well, seeing as I've been toying with a mod I'd been tweaking and running a Monster Island adventure, I guess I'll share a story while I'm at it.
Ingul Bledgriffon the Free Morass, queen ant woman. Basically added animal people to the adventure mode list, plus various tweaked recipes taken from Wanderer's Friend. Turns out 4 arms are quite useful when you can carve bone shields. After a spree of giant-hunting and a futile attempt to locate a marsh titan that wandered from its shrine, I found a labyrinth. As I've found in the past, minotaurs are far more attentive than giants or cyclopes. Apparently a lion-sized bipedal bug is remarkably stealthy.
Little bit of maze-diving and I had one after me, with a second following not far behind. Very first hit pulps the left upper arm, so there goes an alligator snapping turtle shield. A bit of ineffective back-and-forth later, and it grabs me by the head. I try to jab it some more and only manage to get that knockout strike because it wastes a turn taking another swing at me instead of trying to crush my head in.
So I start stabbing at it while I wait for the second to close the distance, soon backing away since the unconscious minotaur was still somehow holding me. Naturally his first punch gibs a leg and floors me. Soon enough I'm back to just barely avoiding blows and getting grabbed fruitlessly when it splatters my spear arm.
So at that point, with it grabbing onto me and about to wrestle me to death, I pulled my dagger out with one of my intact pair of arms. Only one chance, and with a weapon I had no skill in.
So yay, one lucky facestab and both minotaurs are out cold, leaving me to knife them both to death, retrieve my gear. While I'm at it, I celebrate by filling my waterskin using one of the multiple pools of minotaur blood. I'd really wanted to see if I could shank that marsh titan and drink it's blood, but oh well. Speaking of blood, I managed to crawl out of that damn place without bleeding to death, whee.
Naturally I also upgrade my bone armor some, since semi-megabeasts and megabeasts were tweaked to have slightly better body materials than the norm. As for the leather, I was reluctant to replace my scale armor and boots since my scale armor and boots are still more-or-less on par with upgraded leather, at least in some aspects. And last but not least, a minotaur horn crown seems like a fitting trophy after the hardest fight this character's had.