How, specifically does one supposed to adjudicate the following:
A tier 10 mythic guardian takes half damage from all non-mythic sources. However, said guardian is also wearing a ring of friend shield keyed to his cleric cohort, so he was taking only half already.
Does this mean he is only taking one-quarter damage? If so, how and when is this divided up, and how does it work in conjunction with his existing damage reducing abilities, such as Absorb Blow, energy resistance, and damage reduction?
True Defender states that "this reduction is applied after all other reductions in damage".
That part pretty directly states that TD is applied last of everything.
Effectively, that makes it rather bad combined with a shield other effect, since you would take a quarter of the damage and your friend would take half, rather than you just taking half.
It might be reasonable to apply shield other last, but that doesn't seem to be the case based on the wording.
From what I've always seen, if a PC or NPC has multiple abilities interacting with one another they happen in most optimal order, usually chosen by the character's player in question.
Now, the 10th tier guardian ability specifically calls out that it "is applied after all other reductions in damage" and absorb damage says "If you have another ability or effect that reduces damage, reduce the damage with the absorb blow ability before applying any other damage-reducing effects".
By my reading, that means the character in question should be able to stack all different damage reducers BUT absorb blow happens first and true defender happens last.
The character could choose to apply his DR or energy resistance first to lessen the damage to his ally or vice versa.
At least that's my take.