VRChat 2018.2.1 introduced OnOwnershipTransfer trigger. https://docs.vrchat.com/docs/vrchat-201821
> OnOwnershipTransfer - Used to detect when the ownership of an ObjectSync object ha changed
But, this OnOwnershipTransfer trigger fires when the ownership of *any* ObjectSync objects in the scene has changed.
Excepting a case that has only one ObjectSync object in the scene, this is useless. Especially, prefabs can't use this trigger because they can't put assumption of another ObjectSync objects.