You cannot activate D-Formation's second effect when you Special Summon a monster face-down.
Placing 1 D Counter onto "D – Formation" does not start a Chain.
The second effect of "D – Formation" starts a Chain. It does not target.
You cannot activate the second effect of "D – Formation" when you Special Summon a monster face-down.
If an effect is chained that flips the Normal or Special Summoned monster face-down, the effect of "D – Formation" disappears.
If you have 2 or more copies of "D – Formation" with 2 D Counters when you Normal or Special Summon a monster, you can activate the second effect of each "D – Formation".
If a card's effect Special Summons multiple monsters during your Main Phase, you can activate the second effect of "D – Formation". In this case you will select which monster you will apply towards the effect when the effect of "D – Formation" resolves.