Flat Stone

Flat Stone is an unlockable passive item added in The Binding of Isaac: Afterbirth †.

Effects[]

Tears bounce off the floor.
- Whenever a tear bounces, it deals splash damage to all nearby enemies for 25% of Isaac's tear damage.

The bounces increase effective range without affecting the stat, usually by around one third.
Indirectly acquiring Rubber Cement through starting an Eden run or the D4 and D100 counts towards unlocking the item.

Bob's Rotten Head: Will now bounce once, causing two explosions and two gas clouds to appear.
Compound Fracture: Bone tears will bounce normally, and bone shards will only bounce once.
Cricket's Body/ Haemolacria/ The Parasite: Tears release smaller tears every time they bounce.
Dr. Fetus: Bombs bounce, dealing damage to nearby enemies when they bounce.
The Forgotten: The bone club bounces when thrown.
Ipecac: The explosive shot bounces, poisoning and dealing high damage to nearby enemies every time it bounces.
The Ludovico Technique: The tear constantly bounces.
- The Ludovico Technique + Compound Fracture: Bone shards burst on every bounce.
- The Ludovico Technique + Jacob's Ladder: Electricity bursts on every bounce.
Mom's Knife: The knife bounces as it flies away from Isaac. Each bounce splashes, dealing the current damage of Isaac's tears.
Monstro's Lung: All tears bounce simultaneously, greatly increasing reach of the burst.
Mysterious Liquid: Tears leave a pool of creep with each bounce.
Pop!: Eyeball tears bounce repeatedly against the floor when they are about to disappear, but can be knocked by other tears to reset their range, meaning tears can be kept in the air forever as long as they are hit when they are bouncing against the floor.

Brimstone: Overrides Flat Stone.
Compound Fracture: No split tears on bounces.
Dead Eye: Each time the tear touches the ground, there is a chance for the damage bonus to reset, making it nearly impossible to stack or keep it.
Epic Fetus: Overrides Flat Stone.
Incubus: The effective range of Incubus' tears is roughly doubled, with a single bounce in the middle of the flight.
Jacob's Ladder: No electricity on bounces.
Kidney Stone: The stone fired by Kidney Stone doesn't bounce.
Lachryphagy: Overrides Flat Stone.
Tech X: Overrides Flat Stone.
Technology: Overrides Flat Stone.
Technology Zero: Only the last two tears will connect via electricity..
Trisagion: Beams continually shrink and grow. Shrunken beams do roughly 75% of normal beams' damage.

Flat Stone was added in Booster Pack #5, after the initial release of the DLC.
Flat Stone is based on this Steam Workshop item by Maddogs and Joe, originally known as Hydrophobicity.
It seems as though originally, the lasers produced by the Technology items ( Technology, Technology 2, and Tech.5) and Brimstone were meant to synergize, as seen in the concept art of Flat Stone.