From Ryzom Wiki
Yubo plushies are inherently evil entities that seek to infiltrate the inventories of all homins and then devour their hosts from within.
They appear as cute and fluffy plushie versions of the Yubo to seem harmless, and many homins are fooled by this and actively seek to have a yubo plushie in their inventory. The picture on the right shows their true evil face.
As an inventory item, the yubo plushie is called "Teddy". They have 0 weight and 5 bulk and no other stats. They come in all qualities, and that changes absolutely nothing except the number on their icon.
They can be wielded in your right hand like a weapon or crafting tool, but give no bonuses or anything and you can't do anything with them. (Though you can still cast spells while wielding them, but that's no different from casting spells with a crafting tool equipped.)
They're purely to look cute!