Cursed Eye is like a horrible run ender to me, the chance feels like it's 75% to get warped on hit so if you aren't overwhelmingly strong then bosses can be nearly impossible. The charge effect isn't even all that great imo, I had really high Tears when I got it and I really think optimal charge shooting was LESS than I was shooting before, for a lot more input pain. (If you have quad shot+20/20 it might be ridiculously gigantic enough to be good, but even then not worth the warps)
The Solar System challenge is a nightmare if you don't get, like, mini brimstone. :C Some bosses are nearly run-enders if you get them just because getting close is ultra-doom (Don't even want to think about Mom/Mom's Heart; bible plzzzzzzz) I also regret ever unlocking Necropolis, dear mother of jesus it double-spawns on like all of my challenges and it's awful.