Hesserhorn

The hesserhorn is a gigantic aquatic mammal with two large horns on its back; one pointing forward, the other back. Whilst a naturally docile species with little outward aggression, these beasts are known to cause a hefty amount of damage to ships when surfacing due to their bulk, and their horns can easily lead to punctures far too large for an average crew to repair in a timely manner, especially should it get lodged on something, causing the hesserhorn to struggle. For this reason, hesserhorn migratory patterns are observed and warnings are placed in areas of high activity. 
Appearance
Roughly 15 metres in length (discounting horns) and weighing a hefty 12 tonnes, hesserhorns are large, oblong slabs of floating weight. Their skin is a dark blue, mottled with various blueish-green shades of spots. Their corkscrewed horns are a more ashen brown, and the nature of the corkscrewing horns results in a rather hefty tip of around 30cm and around 2 metres in overall length. With the upward angles of these horns and their slightly inward starting point on the back, it only adds a little more than a metre to their effective length either side. Like other aquatic mammals, the hesserhorn has a blowhole, but they also have a number of air sacs beneath their bodies between their flippers. Air isn't stored in them, but instead the expended air is exhaled into them, inflating them as their oxygen supply decreases and acting as a buoyancy device that helps raise them faster.

Diet & Behaviours
Hesserhorns are omnivorous, and renowned for being incredibly lax. They mostly sustain themselves on small sea creatures that swim into its mouth as it gradually floats through the oceans, starting at a low depth and gradually rising as their air supply lessens. That's not to say they don't have the penchant for aggression or the capability of eating bigger game, however their nature tends to lead to this only occurring in instances where they're under threat. In these situations they're preferred method of defence is to get below their attacker, inflate their air sacs all at once and use the momentum to skewer the attacker in the ascent. For this reason, it's advised against aggressive action against hesserhorns even when they actively damage a ship - they can do far more damage if they intend it. They tend to travel in small groups of 2-6, most of which are related to each other. When a hesserhorn fully matures at 5 years old, they will often split off from the group in order to find a mate, at which point the partners will spend the rest of their years together, raising their offspring as time permits. It's reckoned that the full lifespan of hesserhorns is between 15 & 25 years.