Prone

If a creature is knocked prone, they require one turn to stand back up again. If prone on an object that can be laid on, such as a, the creature's effect is renamed to. Creatures that do not have any body part that is feet-like, roots-like, nor contribute any mobility cannot be knocked prone.

The Movement Speed penalty does not have any effect, as prone creatures cannot move and getting back up is an action dependent on Quickness.

Ways to go prone
Creatures can become prone in several ways:

Falling prone in harmful liquids can inflict multiple possible effects on the victim.