Please allow for different difficulty levels. I am finding the regular setting near impossible. The waves move too quickly. Allow a pause button so that players can place towers.
I've got a better idea than towers targeting the enemies with gems: How about let us choose the targeting strategy for each tower, a simple button for each tower on its stats badge that let's us choose: 1. Target enemies with gems 2. Target enemies closest to the gem nest 3. Target closest enemy.
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 "Cursed Treasure 2"){kind=icon}
 "Bloons TD 5"){kind=icon}