The Appa plush in Creatures of Sonaria is part of the Avatar collab reward set, and it gives an in-game equippable plushie effect rather than being just a cosmetic item.

What it does

  • It is an equippable plushie tied to the Appa/Sky Bison event content.
  • Plushies in general provide special stat boosts or effects to creatures in the live game.
  • Based on the available sources, the Appa plush is obtained through the limited-time collab mission and can be kept after unlocking it.

Practical meaning

  • In play, it is meant to give your creature a gameplay bonus, not just a visual accessory.
  • The exact boost for Appa itself is not fully spelled out in the available source snippet, so the safest answer is that it functions as a special stat/effect plushie from the collab.

Source note

  • A recent guide video says you must complete the Sky Bison mission to unlock and keep the sky bison species and an in-game equippable Momo plushy.
  • The general plushie wiki explains that plushies give special stat boosts and effects in the game.

TL;DR: the Appa plush is a limited-event equippable plushie that gives a gameplay bonus, not just decoration.