I'm unclear on several details of how a Shield Guardian works. (MM p. 271)
It is bound to an amulet wearer:
Bound: The shield guardian is magically bound to an amulet. As long as the guardian and its amulet are on the same plane of existence, the amulet's wearer can telepathically call the guardian to travel to it, and the guardian knows the distance and direction to the amulet. If the guardian is within 60 feet of the amulet's wearer, half of any damage the wearer takes (rounded up) is transferred to the guardian.
From the description (outside the stat block):
A shield guardian's solitary focus is to protect the amulet's wearer. The amulet's wearer can command the guardian to attack its enemies or to guard the wielder against attack. If an attack threatens to injure the wearer, the construct can magically absorb the blow, even at a distance.
And it can store a spell:
To do so, the wearer must cast the spell on the guardian. The spell
has no effect but is stored within the guardian. When commanded to do
so by the wearer or when a situation arises that was predefined by the
spellcaster, the guardian casts the stored spell with any parameters
set by the original caster, requiring no components.
My questions are:
Does the amulet wearer have to use a bonus action or anything to
command the guardian?
If the amulet wearer does not issue any explicit commands, does the guardian
act independently with the general goal of protecting the wearer, or
does it act only as commanded by its amulet wearer?
Does the guardian act on its own initiative count?
The text about storing spells states that the spell will be cast by
the guardian with the same parameters as set by the original caster.
Do we assume that the amulet wearer can choose a different target
for the spell at the time it is cast by the guardian?
If the guardian casts "when commanded" — does the guardian cast the
spell on the owner's turn when commanded, or on it's own next turn?
Especially if the former, does commanding it to cast a spell use any
action on the part of the amulet wearer?
The guardian can also cast when a predefined situation arises —
does that mean the guardian can cast as a reaction when the
situation arises? Or does the situation have to be something like
"if on your turn…." ?