If you haven't TOUCHED Gaiden, don't look at this post. This is about IWBTG Gaiden.
In all seriousness though, spoiler alert below. I HIGHLY recommend not viewing this unless you are Kayin or someone else who has made it to the 2nd save point in 1-2.
I found a bug in IWBTGG. I was trying to get past the room in Stage 1-2 with the guy firing a rocket launcher. So i was fooling around, trying to blow up the missile. Which didn't work. Then i hit it with the bionic arm. Immediately, the dude firing it blew up. I was like "OK...?" and started doing that over and over, thinking that was part of the game. Got to the other side of the chasm. Find nothing there. I'm cautious, looking for traps. There are none. I save, then die trying to move on, and find that not only did the bug blow up the first guy, but all the other ones in the room, because there were 2 more. If you absolutely have to see images, I recorded the entire thing. Because I felt like Let's Playing. So yeah, i have 5 screenshots explaining what exactly happened.
The bug itself:
Something i should note about the bug: Hitting the missile sometimes causes it to move in the other direction. Other times it stays on it's original path. Both, however, result in, at the very least, blowing up the first guy. I don't know about the other guys because i didn't make it to the other side of the room on one where the missile kept going.
The other side of the room normally:
The other side after the bug:
While I'm on the subject, before i even started playing, I was already confused. Kayin says press z to jump, x to fire, and x to bionic arm on the download page. This is incorrect, as to bionic arm you need to push c. Just thought i'd throw that out there so no one else gets confused.