Can't find Mom's Box in the shop

[JayK]

Hi guys. I'm trying to unlock the Lost on my 3rd save file now by playing with Isaac and rerolling the shop over and over again until I find Mom's Box for the Missing Poster. However, I'm sure I had 15 runs by now and Mom's Box just doesn't appear. I can't remember it being so rare in the shop. Does anyone know if this is a bug?

[MORCEGUINHO]

I think that's part of the new update. But if you want to unlock The Lost, you can pick up the Mysterious Paper, and try dying in the sacrifice room. There's a 25% chance to unlock it. Good luck.