Note from the Palm: I'm a shark, I'm a shark, I'm a SHAAAAAARK!
Path of the Fin
Tribal communities exist all across the realms, in all manner of locales and climes. While their customs often change, one steadfast certainty, seen time and time again, is the reverence for particular animals local to that tribe. These are often wildly varied; northern tribes may revere the Wolf or the Bear, those of the deserts follow the Hawk or the Jackal, and those of the jungle may aspire to the Ape, or the Tiger. It is in this tradition that the Path of the Fin, island warriors capturing the bloodthirsty essence of the great Shark, arose.
Fin barbarians, as opposed to their land-locked brothers, undergo much in the way of physical transformation when they enter a rage. Starting at 3rd level, while raging, you sprout rows of razor-sharp shark teeth and gain a melee bite attack which deals 1d8 slashing damage on a hit. When you attack a living creature with this bite, you heal a number of hit points equal to half the damage dealt.
A fully grown shark can smell a single drop of blood in the water almost a mile away. At 6th level, you gain an amazing sense of smell. You gain advantage on all Investigation and Perceptions rolls dealing with smell, you can automatically track a single living creature whose scent you know so long as the trail is no older than a week old. By spending a minute concentrating, you can detect the scents of all living creatures in a 100 yard radius, or up to a mile in the water.
Starting at 10th level, your bite attack damage increases to 1d10, and a creature you bite must make a Dexterity save (DC 8 + your proficiency bonus + your Strength modifier) or be knocked prone.
At 14th level, you become a total amalgamation of shark and man. You gain gills, a small dorsal fin, and your skin becomes rough, like that of a shark. You gain a swim speed equal to twice your walking speed, you can breathe underwater, and your armor class increases by 2. Additionally, your bite damage increases to 1d12.