"You failed? Buy this super-duper upgrade and next time you will win!"
I have the suspicious feeling that some levels can only be beaten when you buy the upgrades...
It's easy if you put your cursor in the top right corner and keep making big ones that push the bouncing balls away from the corner. You can keep doing this until you get about 50-60%. Then you just have to choose safe areas and have good timing to fill in the remaining space!
+ if this worked for you! It got 40k points for me!
My tower started to sway with 10 bricks left, so I just held the down arrow and somehow got them all out before it collapsed! Hooray for the impossible badge on my 2nd try!
If you combine the lazer with the rocket launcher, it will launch blue rockets that shoot lazers. Those lazers 1 hit kill everything, so once you get a bunch of blue rockets flying around, it's like having free flying turrets, so you can get both the medium and the hard badge using only 2 turrets!
+ if you try this and it works!
 "ClueSweeper"){kind=icon}
 "Dummy Never Fails"){kind=icon}
 "Man in Gap"){kind=icon}
 "Fade"){kind=icon}
 "Gravitee"){kind=icon}
 "Castlewars"){kind=icon}
 "Sushi Cat"){kind=icon}
 "Bloons Tower Defense 4"){kind=icon}
 "Run"){kind=icon}
 "Grant theft dude"){kind=icon}
 "Gravitee Wars"){kind=icon}
 "Spewer"){kind=icon}
 "filler"){kind=icon}
 "99 Bricks"){kind=icon}
 "UPGRADE COMPLETE!"){kind=icon}
 "The Heist"){kind=icon}
 "Onslaught2"){kind=icon}