ok, the invincibility is fine once you get a few more upgrades.
Personal best right now is 1:02 with 44 bosses killed.
In the "late game" you have so many wall punch upgrades that you can't keep the window at a smaller size. Because of that I can't reach the window of the smiley boss and it hides behind the main window for minutes at a time. I killed 1-2 other bosses DURING one smiley