Sitting

Sitting is an ancient fairy technique, where a humanoid with applicable physiology rests their ass upon a surface or object in order to hold themselves up. This is often utilised in order to free up physical/mental faculties for more efficient rest and increased focus. Other uses include restraining foes, establishing dominance or status, and spumbusing.

Bis:
Bis is often shown sitting on the heads and shoulders of Cassie or Alayna in their pink hair form, and was once shown sitting on Alayna in their white hair form.

It's also implied that Bis's reoccurring threats to flatten Alayna involve the use of sitting.

Alayna:
Alayna has been depicted sitting on multiple misc items, her motivation for doing so is currently unknown. See below for a full list of items Alayna has sat on.

Cassie:
Cassie is depicted sitting on Alayna's head in her thumbnail art, and is confirmed to regularly use the toilet, which she likely sits on.

Sweat Cassie (presumably):
Being a simulacrum of Cassie, Sweat Cassie likely shares this ability, but as of yet has not been confirmed to.

List of items Alayna has sat on
- An empty glass cola bottle containing Bis

- An abstract floating instance of the word "swag" which was hovering over an empty glass cola bottle containing Bis

- A petri dish of soy sauce

- Minecrab Steeb

- Ella Mozzarella Mandela

- Ella Mozzarella Mandela (but bald)

- An advertisement for Pizza Time Explosion, being held by Ella Mozzarella Mandela

- A tiny duplicate of herself

- A small perfect replica of her own ass

- Vriska from the webcomic 'Homestuck'

- Ash

- The abysmal Luigi's Mansion 3DS remake