Played through Bubble Bobble again, this time two player with my brother. After much effort, we beat the final boss, twice, and got the “Bad ending” both times. Most likely my first time beating it.
We played through the levels fairly quickly, using one umbrella. When we got to the boss, it took us a while to get a system that worked. In our final system, I would bounce on bubbles up the side while he ran along the bottom and gave me bubbles. I would pop them to shoot the boss when I could, and bounce up out of the way when he was attacking me. If I ran out of lives, my brother would take over. He’d run back and forth dodging, stack up bubbles on the wall the boss was going toward, then pop them to shoot while he headed away.
My brother actually beat him once, but didn’t realize we needed to pop his bubble until it was too late.
The first time he fully beat him, it told us we got the bad ending a riddle of sorts about a crystal and a door. It gave us the code ‘GEJJJ’. With that, we played the 99th level again and got a crystal. We beat the level and ended up back at the boss, so we fought him again until we beat him, this time with both of us alive. Unfortunately, we got the bad ending again, so we must’ve missed the door part of the riddle. Perhaps for another night.