Reminiscent of a Slime's "typical" look as depicted in various media, Suu adopts this form when lacking sufficient nutrients to maintain her other forms. This can be either due to dehydration or personal choice (eg, she adopts this form when she sleeps).
It is possibly that this is her species' natural form when they are not mimicking the forms and behaviours of other beings.
Suu's "preferred form" is that of an adolescent humanoid female in similar form and stature to Papi.
Suu's other common form; if Suu absorbs enough water (either intentionally or otherwise), she becomes taller and most of the mass goes to her breasts. They are said to be able to hold a fishtank's worth of water.
Kaiju (Giant) Form (Chapter 20)Edit
Dubbed "Giant Suu", or "KaiSuu", by fans, Suu took on this transformation after accidentally falling into a bin of experimental super growth fertilizer.
While in the manga, Suu shows little additional abilities aside from an exponential increase in size (and associated strength) and intelligence, in the anime Suu also gains ridges along her hair tentacles and an atomic breath weapon similar to Godzilla.
Poison Form (Chapter 25)Edit
Similar in nature and appearance to a Green Slime, Suu adopted this "status" while helping Kimihito Kurusu harvest greenery from Kii's Forest; ingesting several plants that contained toxins poisonous to fauna.
Adopting a purple hue, the poisons reacting within her body fizz; resulting in bubbles radiating from her form into the air. While in this form, her speech and mannerisms are laced with blunt, "venomous" remarks, and her typical water spray attacks are additionally laced with poison.
"Hardass" Form (Chapter 31)Edit
Suu gained this form after absorbing mineral-rich water from a Hot Spring. Not much changes in her appearance asside from the fact that she now appears to wear glassess. While the minerals allow her to gain an increase in her intelligence, they also make her adopt a more rigid, "hard", personality. Miia compared it to a "speed-dating demon".
Milf Form (Chapter 36)Edit
Caused by absorbing sea water. Her appearance becomes more mature and her breasts become even bigger. She also becomes notably more lustful and lewd.
Items gained due to changes include glasses made from her "hair" when she absorbs mineral water.