Loses legs; grows snake tail

Organs rearrange
         Stomach, heart, one lung and liver all grow in size and migrate down into the tail, along with most other organs. Other lung remains in the chest cavity but is
         largely unused; torso is now functionally a glorified housing for the esophagus, which is highly elastic

Gains hypnotic rattle
         Six beads, gains a new one each shed. Can be regrown without dying and regenning if cut off or broken

Gains hunger for human flesh and instinct to eat prey whole

Gains affinity for hunting and hiding in water

Art refs:
         x by me