If you install mods before you have defeated Mom (the first time on that save file), the game will lock your achievements. You will still get the item, but the "Mom's Heart" kill won't count toward progression.
Happy dodging.
Modding for The Binding of Isaac: Afterbirth+ and Repentance isn't just a feature; it is a second renaissance. Want Isaac to start with a sword? Want to fight a boss that is literally a sentient meme? Want to turn all the coins into funny frogs? You can do that.
You enter the .
There comes a moment in every Isaac player’s life. You have killed Mom’s Heart 47 times. You have unlocked The Forgotten. You have cried over a bad Soy Milk roll. Now what?