If you want the hard trophy, my suggestion ist to keep right and left arm as dart shooter, and use the pulse laser core. put your money into left/right upgrades until max, Then upgrade your core.In between buy some scinece upgrades (At least two of bluntonium darts, magnet, force field phasing, big bloon sabotage and lastly sharp darts), If you get stuck at a level replay the first 15 levels if you still have less than 90% completion. If you have money to spare buy one epic power, and put the rest into the scoence skills mentioned before. Last boss should not be a problem
 "Bloons Super Monkey 2"){kind=icon}
 "Backyard Monsters (removed)"){kind=icon}
 "Arkandian Revenant"){kind=icon}
 "SteamBirds"){kind=icon}
 "Level Up!"){kind=icon}
 "This is the Only Level"){kind=icon}