I cheated. Do you think it was ok?
When Afterbirth was released, it was bugged up the arse and certain things unlocked too early or wouldn't unlock at all. So, I started a new save file to reset all the issues. Since then, I have done every single kind of run there is, all in hard mode. I've beaten (almost, more in a second) every boss in hard mode, and completed greed mode as every character. Eventually, I only had a couple of hard mega Satan runs left to do. Thing is, I'd already done them, just before I reset my progress.
I got tired of trying to grind them all out again and again with every character, so I just downloaded a 1001% save file to automatically unlock all the achievements I had left. All of the achievements that were left to unlock were the Hard-mode mega Satan kill achievements, and the achievements for beating every boss on hard mode (all that was left was mega Satan).
I'm ok with this, since I'd already put in the work. It's just a shame that my last dozen achievements have all unlocked at the same moment. The question is, would you do the same?