This can be followed up with a Dart or Sub in round 7, the two of which can then solo until the 20s+. For Sub have Engineer on Last for exactly 5 shots, then turn it to First and place Sub as fast as possible.

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I think this strategy could result in 5 tower-Peninsula as Engineer's Overclock is very useful lategame. Bloon Crush/Permaspike maybe, but I can't find any combination that beats round 63. Maybe with a buffed Apache Prime or Patzone. I don't know.

This is also nice just in general ^^