Board Thread:What Would You Do?/@comment-28718853-20190216124627/@comment-36855838-20190225113254

(Thief'd from TV Tropes)

Giant sponges in the 0.34 version. They're not supposed to move, so you can't drive them away from your fort, but somehow they can charge at your dwarves and easily crush them by pushing them around (they're huge, so even a push can crush bones), and are immune to normal weaponry due to lack of body parts and blood. Also, they can spawn in rivers and lakes, too. Normal sponges are like this, but without the killer strength and they can spawn anywhere that has water (giant sponges only live in savage areas). In 0.40, they have been nerfed due to the addition of pulping damage. Sponge tissue is soft and easily destroyed by blunt trauma. They can still hurt your dwarves in the process due to sheer size though.

Edit:

Due to a few of the particulars of combat and skill training, along with an overpowered bite attack, carp in previous versions had the ability to very quickly tear your people to shreds.