I have encountered contradicting information on this matter when browsing the internet. Some sources say:
Booster 0.8: Received from the professor in the labyrinth, if you follow his downward path. Click jump two times to fly. Note: Unable to upgrade to Booster 2.0 on easy mode in Cave Story+.
However, other sources state:
You basically need two things to get the Best Ending. You need the Booster 2.0 and you need Curly.
Does that mean that the best ending cannot be accessed in Easy Mode?
Don't read below, unless you want to get spoiled on how to pull it off.
The Booster 2.0 is unlockable on easy mode (and consequently the best ending). It's no more difficult than unlocking the Booster 2.0 on normal mode. However, if you don't have the Machine Gun, the process is a little more difficult. Take note of the red dot on the block just before the pit where you meet Booster. The red dot marks where you need to start jumping. Hold right all the way while you jump. It is difficult to pull it off, so make sure to save (there is a save point above the pit and the door you came in from) before attempting it in case you screw it up.
If your sources are right, then yes.
You must have the Booster 2.0 to get the Tow Rope and save Curly.
Correct, you can not get the best ending in Easy Mode. Kinda thought it says so at the beginning (in-game), but maybe not.
Your first source is incorrect. It is entirely possible to get the Booster 2.0 on easy mode, and thus get the best ending.
