Hint: keep the bombs and darts/lasers around two levels higher than the tentacles and around the same level. When you obtain the quad smart missile, start upgrading only the tentacles and lasers until the tentacles become maximized and the laser reaches the last level before the death ray. After that, just maximize the bombs.
I just confirmed my theory that the 3-way laser is MUCH more effective than the death ray, not only because it's spread, but it can actually inflict a lot more damage on ceramic bloons and MOABs/BFBs.
I got gold ranking in every level using this strategy.
Also, what's with the broken high scores? The top score os over 1000 times higher than my score with all golds. Am I missing something?
 "Bloons Super Monkey"){kind=icon}
 "Doeo"){kind=icon}
 "Brain Waves"){kind=icon}
 "Meat Boy (map pack)"){kind=icon}
 "Harmony Keeper"){kind=icon}
 "Bloons Tower Defense 4"){kind=icon}
 "Cover Orange"){kind=icon}
 "Heavy Weapons"){kind=icon}
 "Factory Balls 2"){kind=icon}
 "Desktop Tower Defense 1.5"){kind=icon}
 "Frantic"){kind=icon}
 "The irRegularGame of Life"){kind=icon}
 "Hedgehog Launch"){kind=icon}
 "Bubbles 2"){kind=icon}
 "Hit The Jackpot 2"){kind=icon}