Haha, you might actually be the first to find it! Did the second boss ship come down? Here's the playthrough, check at 58:30, it should give you the achievement when you complete the final boss:
I have beaten the second boss multiple times as well, yes, but still no achievement. There are two achievements for the final boss, so am I supposed to get the other achievement for defeating the second form and it's just bugged, or is there something else I need to do?
