https://pbs.twimg.com/media/CgZjFHkWIAA9v72.jpg:orig
Wasted the whole day trying to figure out why this thing refused to work. Turns out I misplaced the memory for the boss and it ended up overlapping an area used to store the game status. Damn.
The screenshot makes it look more exciting than it actually is, so far jumping off the mirror is the only thing the doppleganger ever does.

