Mods and progress

[Jeff]

I have been playing for a while now, and just downloaded my first mod. (the one that tells you what items do)

I read that mods can prevent achievements or progress, but I did a challenge run and it gave teh achievement even though I was using a mod.

Do mods prevent achievements or progress or unlocks?
Is it only ones that affect gameplay that stop them?

Just curious so I don't slow down anything by playing with this mod.

[squat_instructor]

They prevent achievements on a fresh save file until you kill Mom for the first time + they block daily runs, so those need to be done without mods to get related achievements

[Nazemec]

Mods prevent all unlocks/achievements if enabled before the first Mom kill on that save (= unlocking the Womb floors).
They do not prevent anything* once you're past this point.
(The exact same logic applies to enabling the debug console.)

This applies to all mods, whatever they do.
There are a few exceptions, but it relies on how (technically) the mod does what it does. For example, the mod "always Void portal after Mega Satan" (or whatever its exact name is) is known to somehow prevent Mega Satan unlocks.

Edit:
* Except Daily Runs which can't be played at all if mods are enabled, as mentioned by the post above.

[Jeff]

Ok, thanks. I guess I'll check out other mods if they don't cause problems.