Hard mode

Hard mode changes the gameplay compared to Normal in some ways to make it more difficult. When playing in Hard mode, a small red pentagram () appears on the HUD, below the pickups.

Differences[]

2-3 more rooms generate each floor.
Standard rooms with a difficulty of "1" cannot generate.
- Standard rooms with a difficulty of "1" have a reduced chance of appearing.
- Most rooms with this difficulty are very easy, making difficult rooms more common.
Enemies have a base 20% chance to become Champions instead of only 5%; additionally, they only award pickups 33% of the time.
Hearts are 66% less likely to drop after completing a room.
- Hearts are 33% less likely to drop after completing a room.
Only champion bosses will drop hearts; normal bosses will not.
Floors are more likely to have curses.
Blood Donation Machines only give out one coin per use.
- Also applies to IV Bag.
Beggars require a minimum of 6 donations before paying out.
- This doesn't apply to Bomb Bums or Key Masters.
The Shop can be a lower level even if the store upgrades have been unlocked.
The drop rate of soul hearts from blue fires is 10%, while it's 25% in normal mode.
Certain enemies and bosses have increased shot and movement speed.
Dogma does not provide the effect of The Wafer.

Unlocks for Hard Mode[]

Character	Mom's Heart	All completion marks
Isaac
Magdalene
Cain
Judas
???
Eve
Samson
Azazel
Lazarus	Bethany (without losing a life)
Eden
The Lost
Lilith
Keeper
Apollyon
The Forgotten
Bethany
Jacob and Esau
All non-Tainted characters
All characters

Trivia[]

Before update 1.03, the reduced drop-rate affected all pickups (not just Red Hearts).
For update 4.00 hard mode also reduced the amount of tinted rocks appearing. This was removed with 4.01 a few days later.
Most Hard mode unlocks are co-op babies, with the notable exceptions of Godhead, Smelter, Marrow, Mega Mush, Death Certificate and the character Bethany.
Godhead's unlock requirements were extended in later DLCs due to the addition of more completion marks, but it can still be unlocked in the base game using the same method.
None of the tainted characters have unlocks tied to getting all completion marks, apart from Death Certificate.