Sync generally refers to making the cooldowns of your Ultimate Weapons (and Golden Bot) triggering at the same time for exponential coin gains, but can also refer to other strategies achieved by tweaking your cooldowns to match a certain goal.
Let’s use an example to illustrate the power of syncing econ ultimate weapons: imagine that you by default get 1,000 coins from a group of enemies. When these are killed within Black Hole you may receive 11x the amount = 11,000 coins. And if you killed this group of enemies only when Golden Tower was active, you would get 20x (just an example) = 20,000. However, imagine if they were both active at the same time, that would mean that you would get 1,000 x 20 x 11 = 220,000 coins for that same group of enemies. And when you start to take into considerations such as Death Wave, Spotlight, and Golden Bot too, these sync-related coin numbers can get really high.
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But sync does not have to be coin or farming-related. For example, it may make sense for some to sync their Amplify Bot for consistent and enhanced damage in tournaments/farming. And so on.
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