A glitch I discovered while routing the speedrun for this game. You need the red sword powerup, and you need to be on your last star. Then attack an enemy right when it attacks you at the same time as another enemy (or something in the environment) damages you. So you attack, an enemy attacks, and another enemy hits, all on relatively the same frame.

You will lose your powerup, but then certain enemies who come within range of you will die, and at the same time, you'll take damage. This glitch goes away the next time you jump or attack. And you can only recreate this glitch in certain spots due to it requiring specific enemy positions.

I was able to do it on the 2nd level of stage 6 (the enemy base), where it affected walking enemies, not just jumping enemies, and it even broke open a powerup drone. But I wasn't able to recreate it on video.