Okay, I may have accidentally found an Isaac speed run tactic in Wrath Of The Lamb. Sadly, I have no video of me actually doing this, but I can give you a detailed description on how to do this, so I can prove that I'm not full of crap.
So I was going for the Golden/Platinum god achievements, and I was going for all the challenge items. I was on the Lord Of The Flies challenge, and after a couple of attempts, I got a really lucky Bobs Curse and Epic Fetus combo (giving me poison missiles), and wiped the floor with Moms heart.
This is where things get interesting.
I beat Moms heart for the 8th time, giving me Money=Power (a really good item btw). Conveniently, the devil room to open Sheol opened. Since I never got Mom's Knife yet, I decided to go down. Though Sheol is a bit harder then the womb/utero, because of my OP synergy, it might as well have been a walk in the park. I beat Satan, got Mom's Knife, and beat Sheol for the second time. I skipped the Sheol cutscene, because theres really not that much of a point to see a cutscene for the second time.
I was caught off guard, because rather then seeing the Everything is terrible title screen, I was seeing Isaac on the umbilical cord (the title screen you see upon beating Mom's heart for the 9th time). Curious why this was happening, I checked the unlocks page. Sure enough, my future past awaits! I unlocked It Lives. I checked if I got the ending that indicated that In unlocked It Lives. Surprisingly, I did have it. I even went as far as to go and beat The Womb, and who knew? It Lives was the boss I was facing.
So I wanna know, can anyone tell me why this happened? Has anything similar to this (or hell, just a glitch) happened to you? Sorry for the long comment, just wanted to share this. Lets hope I actually get some answers!