Just cheesed my way through Seeing Double challenge. I guess I discovered a bug - 9 lives early (picked up by Esau fwiw) to my surprise let me continue after I ran out of all lives. So I just had to do all of the bosses and rooms without taking damage with infinite retries.
Took me 90 minutes, but hey, I'm happy.
I'm reporting it to Nicalis though.
Some of the rooms took me 5+ minutes and some of the bosses 10+ minutes of continuous attempts.