You place the 3 Spell Counters on “Pitch-Black Power Stone” even if “Royal Decree” is active, so if your opponent chains “Royal Decree” to your “Pitch-Black Power Stone”, or chains “Call of the Haunted” to Special Summon “Jinzo”, you still get 3 Spell Counters on it.
“Pitch-Black Power Stone”’s transfer effect targets.
“Pitch-Black Power Stone” may itself receive additional Spell Counters from effects such as “Apprentice Magician”.
You can use a Spell Counter from a card like “Breaker the Magical Warrior” and replace “Breaker the Magical Warrior”’s Spell Counter with “Pitch-Black Power Stone” on the same turn (and use “Breaker the Magical Warrior”’s effect again that same turn, if you wish).
If you have multiple “Pitch-Black Power Stones”, each can transfer 1 of its Spell Counters per turn.
If you have 1 Spell Counter left on “Pitch-Black Power Stone”, and your opponent activates “Mystical Space Typhoon”, and you chain the transferring effect of “Pitch-Black Power Stone” (a Spell Speed 2 effect), first the transfer effect resolves and the Spell Counter is moved, then “Pitch-Black Power Stone” is immediately destroyed before “Mystical Space Typhoon” resolves.