Attacks » Mirror Move
Can you do Pidgeot EX's "Mirror Move" attack if the opponent's last attack "placed damage counters" (as opposed to "doing damage")?
No. Placing damage counters is an effect. Mirror Move does not copy any other types of effects from the last attack either.
Source: Evolutions FAQ (2016-11-03), TPCi Rules Team (2016-11-03)
Attacks » Mirror Move
If an opponent's attack damages my benched Pidgeot EX, can it do "Mirror Move" during my next turn and attack for the amount of damage it received while on the bench?
Yes, it can.
Source: Evolutions FAQ (2016-11-03), TPCi Rules Team (2016-11-03)
Attacks » Mirror Move | Trainers » Ninja Boy
Let's say I have Machop active with a Focus Sash attached, and my opponent's Mewtwo-EX uses "X Ball" for 360 damage with four Double Colorless Energy and a Muscle Band attached. The Focus Sash leaves Machop with 10 HP remaining. If I then use Ninja Boy to switch Machop with Pidgeot-EX and then use its "Mirror Move" attack, does Pidgeot-EX do 360 damage in return?
Yes, it would. When using Ninja Boy the amount of damage done last turn is remembered by the new Pokemon, so Mirror Move would do 360 damage to your opponent's Active Pokemon.
Source: TPCi Rules Team (2016-11-03)