A piece of coal.
Isaac's face becomes dirtied with coal dust.
Tears turn black and increases damage based on how long tears have been on the screen. The size of Isaac's tears is decreased initially, but increases as damage does. In Rebirth, this is changed so that the tear's damage increases based on its distance from Isaac, an aspect Edmund claims was the original intended use of the item.
- The damage from A Lump of Coal is added when the tear hits, after any damage multipliers.
- If A Lump of Coal is rerolled with The Dice, it will be replaced with a Devil Room item, which will not cost any heart containers.
- With Brimstone, Technology or Technology 2 Isaac's damage will increase by 2 instead of the normal effect.
- Becomes less effective as Shot Speed increases. This is because damage increases based on how long Isaac's tears are on screen, and higher Shot Speed decreases that time.
- Makes Tammy's Head less damaging.
- Turns Mom's Knife black, but does not increase damage.
- Can be very potent if combined with an item that causes tears to home in on a target (e.g. Magician tarot card or Spoon Bender) and if range has been increased by a large amount.
- Sacred Heart - The slow shot speed and homing can allow for a large damage increase with this item.
- IPECAC - Ipecac's long travel time allows for increased damage.
- Can make My Reflection tears much more powerful.
- Reference to the folk tale that any child who is 'naughty' will receive a lump of coal for Christmas.
- Collecting A Lump Of Coal will give the player an achievement for the Gift Pile Steam Event 2011.