Tengu format ruling
Ancient Gear Castle

Card effect (current official text)All "Ancient Gear" monsters gain 300 ATK. Each time a monster is Normal Summoned/Set, place 1 counter on this card. If you Tribute Summon an "Ancient Gear" monster face-up, you can Tribute this card instead, if the number of its counters is equal to or greater than the number of required Tribute(s).
Rulings
(1) Face-up Ancient Gear monsters gain 300 ATK. (2) Each time a monster(s) is Normal Summoned or Set, put 1 counter on this card. (3) If you Tribute Summon an Ancient Gear monster, you can substitute this card for a Tribute(s), if the number of counters is equal to or greater than the number of required Tribute(s).
- The (1) Continuous-like Effect applies to Ancient Gear monsters on BOTH sides of the field.
- The (2) Continuous-like Effect does not start a Chain.
- "Set" means to Set from the hand.
- This card gains counters when a monster is Normal Summoned or Set (from the hand), even if a card effect performs the action (such as Ultimate Offering).
- This card does not gain counters when a monster is Set by a card effect (by "Book of Moon").
- This card does not gain counters when a monster is Special Summoned face-down (by "The Shallow Grave").
- The (3) Continuous-like Effect does not start a Chain.
- While Geartown is active, you can Tribute Ancient Gear Castle with 1 Counter to Tribute Summon Ancient Gear Golem.
- This is not an extra Normal Summon, it only substitutes the monster(s) to be Tributed.
- This effect does not apply for a Tribute Set.
Rulings data courtesy of Format Library — formatlibrary.com. Spotted an inaccuracy? Flag it in the Tengu forum — sourced change requests get reviewed.