OnDeployed(BaseEntity parent, BasePlayer deployedBy, Item fromItem)
Why the 3rd argument?
What is it?

I would expect it is the item being used to place the deployable.

0x89A

I would expect it is the item being used to place the deployable.

If I deployed by plugin I should send null?

Unless its a Signage or PhotoFrame, null works. Otherwise these two require an item.