Flat Stone

Flat Stone is an unlockable passive item added in The Binding of Isaac: Afterbirth † (Booster Pack #5).

Effects[]

Tears bounce off the floor as they travel. Whenever a tear bounces, it creates a small splash that deals 25% of Isaac's tear damage to enemies.

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.
Dropping Rubber Cement as Tainted Isaac and picking it back up counts towards unlocking the item.
Should be avoided when going for The Beast fight, as tears will fall straight to the ground during the final fight. Even with Continuum the tears will fall into the lava and disappear instead of falling back down from the top like they would in a crawlspace.
Should be avoided when going for Mother, as encountering Rotgut's 2nd phase becomes near impossible to hit.

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. Works even with Tech X .
Ipecac: The explosive shot bounces, poisoning and dealing high damage to nearby enemies every time it bounces.
The Ludovico Technique: The tear constantly bounces.
- With Compound Fracture, bone shards burst on every bounce.
- With Jacob's Ladder, electricity sparks 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/Epic Fetus/Tech X/Technology: 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.
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: Initial tears will act as normal for Lachryphagy but tears from burst will bounce.
Ocular Rift: Only the first bounce creates a rift. (Jy-Are47, add image and confirm info)
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 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.