When you pause (start/enter) and tab over to the left-most menu (L/A on keyboard), you can then press ESC and scroll down to the option that takes you back to the main menu.
Will take a look at the vine knockback issue, I think I missed a bit of code in the hitstun state relating to the slopes.
Yeah the difficulty actually used to be much higher, but in early pre-release playtesting, I had to tone it down quite a lot. I definitely plan on upping the difficulty as you get further in the game, and later on, I'd like to implement a "customized game" feature that will let you adjust difficulty more directly.
Thank you so much for your support and feedback, it means a lot!!