Pyro Clock of Destiny

 This is the only card that can change a card's turn count.

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When this card first debuted in the OCG, it had only 5 legal targets: Lightforce Sword, Nightmare's Steelcage, Steel Scorpion, Swords of Revealing Light, and Zone Eater".

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OCG Rulings

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The effect does not target.: Pyro Clock of Destiny

It cannot be activated during the Damage Step.

Cards that apply their effect for 3 turns after activation, like "Deck Devastation Virus", are cards that count turns.

Cards that resolve when the 2nd Standby Phase after activation is reached, like "Gold Sarcophagus", are not cards that count turns.

Because the effect of "Doom Virus Dragon" counts turns, "Pyro Clock of Destiny" can be activated and increase its turn count.: Can "Pyro Clock of Destiny" be activated against the effect of "Doom Virus Dragon"?

Because the effect of "Time Magic Hammer" counts turns, "Pyro Clock of Destiny" can be activated and increase its turn count. Furthermore, if "Pyro Clock of Destiny" was activated during the Draw Phase or Standby Phase of the "Nth turn after this effect's activation (N = the result)", because the turn count is increased, the "Standby Phase of the Nth turn after this effect's activation (N = the result)" has already ended. (Therefore, the banished monsters remain banished, and cannot return to the field.) Likewise, if "Pyro Clock of Destiny" was activated during the Main Phase or End Phase etc. of the turn before the "Nth turn after this effect's activation (N = the result)", because the turn count is increased, the "Standby Phase of the Nth turn after this effect's activation (N = the result)" has already ended. (Therefore, the banished monsters remain banished, and cannot return to the field.): Can "Pyro Clock of Destiny" be activated against the effect of "Doom Virus Dragon"?

Semi-Official

Based on the OCG text, "Pyro Clock of Destiny

Previously Official Rulings

You can use "Pyro Clock of Destiny" to advance the turn count by 1 for these cards: “Deck Devastation Virus”, "Swords of Revealing Light", "Lightforce Sword", or "Final Countdown".The latest print of "Lightforce Sword" has Problem-Solving Card Text which indicates that its effect counts Standby Phases rather than turns.

Mentions in Other Rulings

Final Countdown:" You can activate "Pyro Clock of Destiny" to advance the turn count by 1 for "Final Countdown". "Final Countdown" does not have to be on the field when you use "Pyro Clock of Destiny".

Final Countdown:" When you activate "Final Countdown", and your opponent activates "Final Countdown" during his next turn, and then uses "Pyro Clock of Destiny" to advance his "Final Countdown" by 1, both "Final Countdowns" win at the same time and the Duel is a DRAW.

Future Fusion:" "Future Fusion's" effect counts Standby Phases, not turns, so "Pyro Clock of Destiny" would have no effect.

Wave-Motion Cannon:" You cannot use "Pyro Clock of Destiny" with "Wave-Motion Cannon".