That Blue Roflcopter isn't required to beat the level, but it's for two Green Apples. Fall down on the left side, shoot a Splapple so it hits the slant and sends the Roflcopter downwards, then double jump back up and use the red Roflcopter to get back up onto the platform before you die. After that, drop down following the line of Gropples. You should land on the Blue Roflcopter, now ready for use (you need to direct it to the left).
Once you land on the Roflcopter, direct it to the left and you'll eventually come to a platform with a green button on it. Press it and then go to where the arrow is pointing.
-Stay on the far left side of the room
-Focus on the toasters when the boss is right above you
-Focus the boss at all other times
-Focus on the toasters when there's a Hot Toaster present
I think I had 6 or 7 Splapple Burst when I fought the boss myself, so upgrade to that by replaying The Rocket or something.
I had 10 Splapple Burst and 33 Max Splapples when I playtested it. For easy purchases, just keep buying discounts until each price is lowered down to 1 Gropple. That's how I bought most of it.
A good strategy is to go to The Gauntlet, hit all the yellow buttons, return to level select (CTRL) and repeat.