After dwelling in the iron-rich swamps of Hisui for generations, Goomy in the region have developed the ability to incorporate it into their bodies as shells. Mixing with the mucus they naturally secrete, it hardens into a composite material akin to steel. This is a humorous return to form for the species, having likely evolved to lose their shells from a past ancestor only to regain them once again.

Like most mollusks, these shells serve to protect the Pokémon from harm, and the case of Hisuian Sliggo, their armor is nigh-impenetrable to even the strongest claws and beaks. The durability comes at a cost, however, and the extra weight makes it difficult for these Pokémon to maneuver. In consequence, Hisuian Sliggoo only move when absolutely necessary, spending long stretches of time rooted in one spot; when danger arrives, they simply tuck their heads into their shells and wait for it to pass. Perhaps because of this, Hisuian Sliggoo frequently appear to be melancholic and even exhausted with the world. Indeed, they were a common symbol of dejection in Hisuian literature.

And as it's Kalosian counterpart, The Hisuian Sliggoo's eyes devolved when evolve, and it relies on its other senses, specifically its four horns, which act as a radar system to detect sound and smell.

You were walking around until you didn't noticed the Hisuian Sliggoo lying in the floor, so you almost tripped by it's shell.

From a small oriffice of the Shell, The Hisuian Sliggoo let out its head, neck, and nubby undeveloped arms to peek outside. "Looking" at you with that typical melancholic "happy" face of it's.