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.
- 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
- 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.