19 Jan 2018
If Golden Guardian leaves the battlefield before its activated ability has resolved, it won't be returned to the battlefield when the ability resolves.
19 Jan 2018
Once Golden Guardian's activated ability has resolved, it will return to the battlefield transformed if it dies for any reason in that turn.
19 Jan 2018
If the target of Golden Guardian's activated ability isn't a legal target as that ability resolves, or if Golden Guardian has left the battlefield, neither creature will deal or be dealt damage.