Don't refrain from selling plants in order to move faster towards the enemy. This strategy helps with stopping him from getting too many crystals. Only relevant for getting the gold medals imo. Standard levels are easy.
for the impossible badge practice each level until you can finish it in a reasonable time before attempting the speedrun. If you go straight for the speedrun it can be frustrating
I justed aced level 4 after countless. The suicide ] method didn't work for me since I can't release the ball out of the gaming area. So I decided to try aiming at the left torch after reading a comment of someone that acing the level is possible without the 'suicide method'. It just would take "a thousand tries". After maybe 2 hours of trying in all kinds of setups I almost gave up took a break and then nailed it. With pure luck the fireball lit the left torch shot over to the right underneath toad, bounced up just high enough to light up the right torch.
 "Crush The Castle 2 PP"){kind=icon}
 "Kaleidoscope Reef"){kind=icon}
 "Symbiosis"){kind=icon}
 "Sprout"){kind=icon}
 "Ring Pass Not"){kind=icon}
 "Portal: The Flash Version"){kind=icon}
 "Amidst the Sky"){kind=icon}
 "Utopian Mining"){kind=icon}
 "Beam Ball"){kind=icon}
 "Super Stacker 2"){kind=icon}
 "My \"Dear\" Boss"){kind=icon}
 "Pyro"){kind=icon}
 "Aground"){kind=icon}
 "Tactical Assassin 2"){kind=icon}