Invincibility Glitch

[THEBARRELROLL]

Step 1: Go to level 2
Step 2: Make sure you have one HP
Step 3: Go to the top of the third tower on the second screen
Step 4: Align yourself with the knight so he hits you onto the switch

The animation will play, and as soon as it's over, you'll be invincible.
Ta-da!

[*Emelia K. Fletcher]

Post it here, but nice catch if it hasn't already been discovered.