Ancient Gears are centered around repeated summons of their boss monster, Ancient Gear Reactor Dragon. The spells Geartown and Ancient Gear Fortress both facilitate Reactor special summons, while Middle Age Mechs and Ancient Gear Wyvern can set up simple normal summons. Most of the trap lineup consists of ways to destroy Geartown and Fortress, with minor defense to round out the deck.
Average size: 20 cards
Top 16 - MCS 17 - April 6, 2019 - AutumnLeaf
Geartown can "miss the timing" if destroyed on Chain Link 2 or higher. Fortress cannot miss the timing no matter when it's destroyed.
Fortress only protects your monsters while it's on the field. If you destroy Fortress to summon a Reactor, that Reactor will be vulnerable to targeting effects like Paleozoic Canadia and Enemy Controller.
There is no window of activation for your opponent's cards between Reactor attacks. Furthermore, your opponent cannot respond to the summon of a Reactor off another Reactor's destruction effect before you attack again.