Rocks

Blocks movement and projectiles unless the player has flight or spectral tears, respectively.
Can be destroyed with explosions and certain items like the Notched Axe, The Nail, Leo, or Thunder Thighs.
Can fill in a 1-block wide gap when pushed in the right direction by an explosion, or with one of the abilities that allows destruction by walking onto the rock.
- Note: With these items, it is important to walk in the direction of the gap.
Small chance to reveal a Crawl Space when destroyed.
Destroying 100 rocks will unlock the Lucky Rock trinket.

Tinted Rocks

Sometimes referred to as "Marked Rocks", they are always marked with an "X", and in some levels slightly tinted/discolored. These rocks are much less noticeable in Womb, Utero, and Scarred Womb due to them being the same color as the surrounding rocks, but can still be distinguished by the "X" on the bottom right. Only one tinted rock can spawn per room.

Destroying 10 Tinted Rocks will unlock Mr. Mega.
Destroying 100 Tinted Rocks will unlock The Small Rock.
Multiple tinted rocks can spawn in one room by using XVI - The Tower?

Found in: Every Stage

Tinted Rocks have a chance to spawn 1-3 of the following when destroyed:

Soul Hearts
Keys
Bombs
Locked Chests (only one)
Red Chests (only one)
Chests (only one)
Tinted Rock Spiders (Mines and Ashpit only)
A combination of any of the items mentioned above
The Small Rock (after it has been unlocked)
- Not picking up The Small Rock right after it spawned doesn't prevent other tinted rocks from spawning it again. Even though the chances are very small, this can be exploited to obtain multiple Small Rocks.

Super Special Rocks

Super Special Rocks are Tinted Rock variants whose smaller marks and lack of discoloration make them much harder to spot. Super Special Rocks take two bombs to blow up and drop the contents of two Tinted Rocks, with the exception that a single chest or The Small Rock appear without extra rewards.

Only one super special rock can spawn per room, and normal tinted rocks cannot appear in the same room.

In Chapter 4 and Chapter 4.5, Super Special Rocks are almost identical to Tinted Rocks, making them easier to spot in these chapters.

Super Special Rocks are unlocked by the achievement 5 Nights at Mom's, which requires getting a 5-win streak, using a different character each time. This number can be reduced to 3; see the Notes section of the Achievements page.

Bomb Rocks

Act like rocks.

Found in: Small chance of replacing any rock on any chapter.

Bomb rocks can be found anywhere a normal rock can spawn. They can only be destroyed by explosions and "stompy" items, like normal rocks. When they are destroyed, they create an explosion. Note that destroying a bomb rock next to a hole does not create a bridge as with normal rocks.

Spiked Rocks

Spiked Rocks are variants of normal rocks which hurt Isaac on contact, even if he's flying.
They can fill in a 1-block wide gap like ordinary rocks, but the spikes will remain and Isaac will take damage as he steps on them. If they are located in a room with Pressure Plates, after all the plates are pressed, the spikes will retract into the interiors of the rock. If a Crawl Space is generated with the same rock used to fill a gap, the bridge will not be spiked.

Flat File will remove the spikes from the rocks.

If spiked rocks are crushed by being Stompy, having Leo or Thunder Thighs, or using The Nail, they do not always deal damage, depending on Isaac's speed, size, and the angle they are touched from.

Found in:

Dross
Mines

Notes

If a Spiked Rock is used to fill in a gap, stepping on the created spiked path will deal a full heart of damage. This damage is considered self-damage (it will not affect Angel/Devil Deal chances and items such as Paschal Candle). Touching Spiked Rocks, however, will not count as self-damage.

Fool's Gold Rocks

Act like rocks. They have a small chance of replacing normal rocks, sometimes in small clusters, once unlocked.

Unlocked by: Defeat Mega Satan as Tainted Lilith

Fool's Gold Rocks will spawn the following when destroyed:

2-4 Pennies

Urns

Act like rocks.

Found in:

Shop
Arcade

Angel Room

When urns are destroyed, the following events can occur:

Nothing (68.00%)
One random coin spawns (4.84%)
Two random coins spawn (4.84%)
Swallowed Penny spawns (2.50%) (can only happen once per run)
A Quarter spawns (0.50%) (can only happen once per run)
One spider spawns (9.67%)
Two spiders spawn (9.67%)

Notes

If spiders spawn from destroying an urn after clearing a room, they will disappear if Isaac leaves and re-enters the room.

Mushrooms

Act like rocks.

Found in:

When mushrooms are destroyed, the following events can occur:

Nothing (68.00%)
One Pill spawns (9.67%)
Liberty Cap spawns (2.50%) (can only happen once per run)
Magic Mushroom spawns (0.33%) / Mini Mush spawns (0.25%)
- Only one of each collectible will drop per run. However, it is possible to get both collectibles in the same run.
- There is a 2.72% chance for a mushroom in a Secret Room to drop Wavy Cap instead of a Magic Mushroom or Mini Mush. Only one will drop per run.
One poisonous gas effect spawns (19.33%)
- This effect knocks Isaac back and deals half a heart of damage. (It does not count as an explosion.)

Skulls

Act like rocks.

Found in:

When skulls are destroyed, the following events can occur:

Nothing (68.00%)
One random card / rune spawns (9.67%)
One Black Heart spawns (2.50%)
Dry Baby / Ghost Baby spawns (0.25% chance each)
- Only one of each collectible will drop per run. However, it is possible to get both collectibles in the same run.
One Host enemy spawns (19.33%)

Notes

Prior to Booster Pack #5, skulls had a chance of spawning Mushrooms instead of Hosts.

Marked Skulls

Act like rocks.

Unlocked by: Defeat Mother

Once unlocked, a single skull marked with a small "x" will appear in Depths, Necropolis, and Dank Depths II or XL. When destroyed, it will drop 0 - The Fool.

If Isaac has Little Baggy, it will drop an identified Telepill. If Isaac also has False PHD, it will drop an identified ??? pill.

Notes

Cannot be re-rolled by D12.
Marked Skulls may spawn in Red Rooms on Depths, The Void, Necropolis, and Dank Depths, even while not in the II or XL floor.
Marked Skulls have different appearances when spawned on other floors, e.g. manually via the console or during the DELETE THIS challenge. Some of these are Cut Content from the original game.
- For example, it will appear as a white urn in Basement, as a red mushroom in Caves, or a horizontally flipped polyp in Womb.
- It will appear as a regular bucket in Dross with no visual difference.

Polyps

Act like rocks.

Found in:

Womb
Utero

??? (blue appearance)

When polyps are destroyed, the following events can occur:

Nothing (68.00%)
Random heart (5.10.0) spawns (9.67%)
Umbilical Cord spawns (2.50%) (can only happen once per run)
Blood Clot / Placenta spawns (0.25% chance each)
- Only one of each collectible is encounterable per run. However, it is possible to get both collectibles in the same run.
A ring of 6 red projectiles and a puddle of red creep (19.33%)

When polyps in the Corpse are destroyed, the following events can occur:

Nothing (68.00%)
Rotten Heart spawns (9.67%)
Lil Larva spawns (2.50%) (can only happen once per run)
Rotten Baby or Rotten Meat spawns (0.25% chance each)
- Only one of each collectible is encounterable per run. However, it is possible to get both collectibles in the same run.
Launches 6 Small Maggots in all directions and a puddle of green creep (19.33%)

Buckets

Act like rocks.

Found in:

When buckets in Downpour are destroyed, the following events can occur:

Nothing (68.00%)
One random coin spawns (4.84%)
Two random coins spawn (4.84%)
Swallowed Penny spawns (2.50%) (can only happen once per run)
Leech spawns (0.50%) (can only happen once per run)
One Strider spawns (4.83%)
Two Striders spawn (4.83%)
One Small Leech spawns (4.83%)
Two Small Leechs spawns (4.83%)

When buckets in Dross are destroyed, the following events can occur:

Nothing (68.00%)
One random coin spawns (4.84%)
Two random coins spawn (4.84%)
Butt Penny spawns (2.50%) (can only happen once per run)
The Poop spawns (0.50%) (can only happen once per run)
One Drip spawns (4.83%)
Two Drips spawn (4.83%)
One Small Leech spawns (4.83%)
Two Small Leechs spawns (4.83%)

In addition to these rewards, whenever a full bucket (i.e. filled with water or filled with poop) is destroyed or picked up by a Polty, 6 projectiles will always spawn in a small radius.