Necropolis

Necropolis is the alternative chapter of the Depths. It is a dark environment infested with insects.

Necropolis is unlocked by defeating every boss from The Depths at least once.

The boss of Necropolis II is always Mom.

After A Secret Exit is unlocked, a door will appear in Necropolis I's Boss Room upon defeating the boss, leading to the Mausoleum / Gehenna. This door requires two hearts to be opened (except on Lost characters). Unlike Angel Rooms and Devil Rooms, this door never disappears. Also after this achievement is unlocked, a Strange Door in the starting room of Necropolis II will appear. This door leads to Mausoleum / Gehenna II before entering the Ascent.

Monsters

Entity	ID	Description
Baby	38.0	Slowly floats towards Isaac and fires a blood shot at him. Occasionally teleports and reappears elsewhere.
Begotten	251.0	Starts attached to the wall or an obstacle. After a while, it detaches, firing 6 blood shots in all directions, turning the room dark, becoming invisible and chasing Isaac. Briefly becomes visible upon getting hit.
Boil	30.0	Stationary enemy that decreases in size when hit, but regenerates to its full size until fully destroyed. Fires multiple short-ranged blood projectiles in random directions when fully swollen.
Gut	30.1	Stationary enemy that decreases in size when hit, but regenerates to its full size until fully destroyed. Fires Ipecac shots in random directions when fully swollen.
Sack	30.2	Stationary enemy that decreases in size when hit, but regenerates to its full size until fully destroyed. Occasionally spawns Spiders when fully swollen.
Walking Boil	88.0	Does not shrink or regenerate. Walks around aimlessly and fires multiple short-ranged blood projectiles in random directions.
Walking Gut	88.1	Does not shrink or regenerate. Walks around aimlessly and fires Ipecac shots in random directions.
Walking Sack	88.2	Does not shrink or regenerate. Walks around aimlessly and occasionally spawns Spiders.
Bony	227.0	Wanders around the room and throws a bone at Isaac when he is in sight.
Death's Head	212.0	Invulnerable enemy that moves diagonally around the room, dealing contact damage. Dies when the room is cleared.
Brain	32.0	Slowly crawls around the room, leaving a trail of Red Creep.
Buttlicker	89.0	Can start attached to other Buttlickers and erratically moves around the room, similar to Larry Jr..
I.Blob	15.2	Randomly wanders around the room, firing 8 shots in all directions.
Dip	217.0	Slowly dashes in random directions, dealing contact damage.
Squirt	220.0	Dashes towards Isaac and deals contact damage. Spawns 2 Dips upon death.
Dinga	223.0	Slowly moves around the room, occasionally hopping to spawn Dips or fire 8 Brown shots in all directions. Splits 2 Squirts upon death.
Embryo	77.0	Aimlessly hops around the room, dealing contact damage.
Pale Fatty	208.1	Slowly walks towards Isaac. Occasionally farts and shoots 6 blood shots in all directions. Has a chance to turn into a Blubber upon death.
Fat Sack	209.0	Slowly walks towards Isaac. Occasionally leaps off-screen and attempts to land on Isaac, leaving a puddle of Red Creep and shooting 6 blood shots in all directions where it lands. Has a chance to turn into a Blubber upon death.
Blubber	210.0	Walks around aimlessly and randomly spews a cluster of blood shots in all directions. Has a chance to turn into a Half Sack when killed.
Half Sack	211.0	Wanders around aimlessly and leaves a trail of Red Creep.
Fly	13.0	Hovers in place. Does not deal contact damage and is harmless, but can turn into Pooters if they stay around Poop.
Attack Fly	18.0	Red fly that follows Isaac and deals contact damage.
Eternal Fly	96.0	Invulnerable fly that circles Corny Poop and various monsters. Deals contact damage. Turns into a vulnerable Attack Fly after the object or monster it circles is destroyed.
Pooter	14.0	Slowly drifts toward Isaac, occasionally firing a single blood shot at him. Does not deal contact damage.
Super Pooter	14.1	Slowly drifts toward Isaac, occasionally firing two blood shots in a V-formation at him. Does not deal contact damage.
Full Fly	249.0	Flies toward Isaac erratically, dealing contact damage. Releases 6 bullets in all directions upon death.
Boom Fly	25.0	Flies across the room in straight diagonal lines, dealing contact damage. Explodes upon death.
Red Boom Fly	25.1	Flies across the room in straight diagonal lines, dealing contact damage. Creates a ring of 6 blood shots upon death.
Sucker	61.0	Flies slowly towards Isaac, exploding into 4 shots in the cardinal directions upon death.
Spit	61.1	Flies slowly towards Isaac, firing an Ipecac shot towards Isaac upon death.
Gurgle	87.0	Walks towards Isaac, dealing contact damage and periodically firing Ipecac shots at him; they are immune to this explosion, but other enemies are not. Can turn into a Splasher upon death.
Rotty	226.1	Slowly walks towards Isaac, leaving short-lasting Red Creep behind itself. Spawns a Bony or two Attack Flies upon death.
Nulls	252.0	Walks towards Isaac, dealing contact damage. Upon getting near Isaac, it will open its eyes, though its speed doesn't change. Fades into and out of visibility.
Globin	24.0	Chases Isaac, dealing a full heart of contact damage. Upon taking enough damage, it collapses into a pile of goo, which can be killed. Will regenerate after a short period of time if not killed quickly.
Gazing Globin	24.1	Quickly chases Isaac, dealing a full heart of contact damage. Upon taking enough damage, it collapses into a pile of goo, which will slide away from Isaac and can be killed. Will regenerate after a short period of time if not killed quickly.
Guts	40.0	Attaches itself to a wall or obstacle and rolls around it.
Mama Guts	57.1	Slowly moves around the room, occasionally hopping and firing 8 large blood shots in all directions. Splits into 2 Guts upon death.
Grub	239.0	Erratically moves around the room like Larry Jr. and charges at Isaac when he gets within its line of sight. Spawns Maggots, Chargers, or Spitties upon death, one for each of its segments.
Gurgling	237.0	Charges towards Isaac when he lines up with them, leaving a trail of Red Creep and shooting 6 blood shots.
Keeper	86.0	Hops around the room, firing 2 blood shots in a V formation at Isaac. Upon damaging Isaac, Isaac drops 2 coins on the ground but loses 3.
Hanger	90.0	Floats around the room, firing 3 spread blood shots at Isaac. Upon damaging Isaac, Isaac drops 2 coins on the ground but loses 3. Spawns with an Eternal Fly circling around it.
Flaming Hopper	54.0	Quickly hops around the room, doing contact damage. Covers a larger distance than the regular Hopper.
Leaper	34.0	Hops around the room, doing contact damage. Occasionally jumps high into the air, dropping down onto Isaac's position while firing 4 blood shots in the cardinal directions.
Psychic Horf	248.0	Stationary enemy that fires a homing shot at Isaac when he gets in range of them.
Host	27.0	Stationary enemy that is normally invulnerable. Raises its head up when Isaac gets close, revealing a fleshy stem that can be damaged. Upon raising its head, it will fire 3 blood shots in a spread and lower its head again.
Red Host	27.1	Stationary enemy that can be damaged even when its head is lowered. Fire 5 spread blood shots when it raises its head.
Mobile Host	204.0	Acts like the Host, but follows Isaac and deals contact damage.
Flesh Mobile Host	247.0	Acts like the Red Host, but follows Isaac and deals contact damage.
Kamikaze Leech	55.1	Quickly charges towards Isaac when he gets in its line of sight. Explodes upon death.
Knight	41.0	Moves erratically around the room and charges towards Isaac when in line of sight. Can only be damaged from behind.
Floating Knight	254.0	Behaves like the Knight but slower, and can fly over all obstacles.
Maw	26.0	Slowly floats towards Isaac, firing a blood shot at him when he is in their range.
Psychic Maw	26.2	Slowly floats towards Isaac, firing homing shots at him when he is in their range. Spawns with an Eternal Fly orbiting around it.
Mask + Heart	93.0	The Mask is invulnerable and moves around erratically, charging at Isaac when he lines up with it. The Heart avoids Isaac and fires 4 blood shots in the cardinal directions when Isaac gets near. Killing the Heart will automatically kill the Mask.
Mr. Maw	35.0	Walks towards Isaac and attacks by launching its head towards him. Turns into a Maw or Gusher upon death depending on the killed body segment. Occasionally separates at will.
Mom's Hand	213.0	Falls from the ceiling. If it lands on Isaac, it deals damage and teleports him back to the spawn room of the floor. Entering a room containing Mom's Hand will warn Isaac with Mom's laugh.
Hive	22.0	Wanders around the room, avoiding Isaac and spawning Attack Flies if he gets close. Spawns a large number of flies on death, which can be Flies, Attack Flies, and/or Pooters.
Nest	205.0	Wanders around the room, avoiding Isaac and spawning Spiders if he gets close. Spawns a Big Spider or Trite upon death.
Nerve Ending	231.0	Static enemy which acts as a meat shield.
Night Crawler	255.0	Pops out of the ground in random locations and fires four short-range shots that spiral outwards if Isaac is in sight.
One Tooth	234.0	Follows Isaac and periodically dashes towards him when it gets close. Deals contact damage.
Spider	85.0	Erratically moves around the room. If Isaac gets close to it, it chases him, trying to deal contact damage.
Big Spider	94.0	Erratically moves around the room. If Isaac gets close to it, it chases him, trying to deal contact damage. Spawns two Spiders upon death.
Ticking Spider	250.0	Crawls around the room erratically, following Isaac and dealing contact damage. Can jump small distances. Explodes upon death.
Trite	29.1	Quickly leaps towards Isaac and deals contact damage.
Ragling	246.0	Quickly leaps towards Isaac and deals contact damage. Randomly shoots two purple shots that orbit around it.
Baby Long Legs	206.0	Runs away from Isaac and frequently spawns Spiders.
Wall Creep	240.0	Crawls along walls to try to line up with Isaac and shoots three blood shots in a line.
Blind Creep	242.0	Randomly crawls along walls and shoots three spread blood shots.
Rage Creep	241.0	Slowly crawls along walls to try to line up with Isaac and shoots a Brimstone laser.
Splasher	238.0	Walks aimlessly around the room, firing Ipecac shots in random directions.
Swarmer	91.0	Slowly floats around the room, spawning several Attack Flies. Spawns Pooters upon taking damage. Spawns a Boom Fly upon death.
Tumor	229.0	Moves around the room diagonally, occasionally firing 6 blood shots in all directions. Fires more often upon getting damaged.
Psy Tumor	253.0	Moves around the room diagonally, occasionally firing 6 homing shots in all directions. Fires more often upon getting damaged.
Vis	39.0	Randomly wanders around the room. Pauses to charge and fire a Brimstone laser when Isaac gets in its line of sight.
Double Vis	39.1	Randomly wanders around the room. Pauses to charge and fire a Brimstone laser which fires from both sides when Isaac gets in its line of sight.
Chubber	39.2	Randomly wanders around the room. Pauses to fire a Charger that deals one heart of damage when Isaac gets in its line of sight. The Charger is invulnerable, blocks Isaac's tears, has limited range, and flies back to the Chubber.
Wizoob	219.0	Disappears, then appears near Isaac and spits a cluster of spectral tears at him.
Lil' Haunt	260.0	Floats toward Isaac and occasionally fires a blood shot at him, predicting his movements.
Poky	44.0	Slides around the room aimlessly, damaging Isaac by contact. Disappears when the room is cleared.
Slide	44.1	Quickly slides towards Isaac when he gets in its line of sight, then moves slowly back to its original position. Cannot be destroyed.
Wall Hugger	218.0	Moves around the room like Guts, damaging Isaac by contact. Cannot be destroyed.
Stone Grimace	42.0	Stationary and invulnerable monster that occasionally fires a blood shot at Isaac. Stops firing when room is cleared.
Vomit Grimace	42.1	Stationary and invulnerable monster that occasionally fires an Ipecac shot at Isaac. Stops firing when room is cleared.
Constant Stone Shooter	202.0	Stationary and invulnerable monster that continuously fires shots in a single direction.
Gaping Maw	235.0	Stationary and invulnerable monster that sucks Isaac towards it, along with Isaac's tears and enemy projectiles.
Blue Boil	298.0	Stationary enemy that decreases in size when hit, but regenerates to its full size until fully destroyed. Fires 1-3 blood shots towards Isaac when fully swollen.
Dank Death's Head	212.1	Moves diagonally around the room, dealing contact damage. Needs to be killed to complete the room.
Mega Clotty	282.0	Slowly moves around the room, occasionally hopping and either firing 6 blood shots in all directions, leaving a puddle of Red Creep, or spawning a Clotty or a collapsed Globin. Splits into two Clotties upon death.
Corn Mine	295.0	Goes off when destroyed or after some time, then releases a cloud of poisonous gas and fires corny shots in eight directions.
Flaming Fatty	208.2	Slowly walks towards Isaac. Occasionally farts, which pushes Isaac and adjacent enemies away and spawns a damaging flame. Has a chance to leave behind a damaging flame upon death.
Conjoined Fatty	257.0	Slowly walks towards Isaac. Occasionally pauses to fart out a line of damaging Green Creep towards Isaac. Chance to turn into a regular Fatty upon death.
Hush Fly	296.0	Gathers with other Hush Flies to form certain patterns. If spawned by Hush, can chase Isaac or orbit Hush. Deals contact damage.
Greed Gaper	299.0	Walks towards Isaac, dealing contact damage.
Blue Gaper	297.0	Walks towards Isaac, dealing contact damage.
Black Globin's Head	279.0	Slides towards Isaac, leaving a trail of damaging Red Creep.
Black Globin's Body	280.0	Walks aimlessly around the room, occasionally spawning spiders.
Black Bony	277.0	Wanders around the room and throws three bones in a row at Isaac when he is in sight. Explodes upon death.
Drowned Charger	23.1	Slowly moves around the room, charging at Isaac when he gets in its line of sight. Explodes into four blood shots in the ordinal directions upon death.
Drowned Boom Fly	25.2	Flies across the room in straight diagonal lines, dealing contact damage. Upon death, explodes and fires four blood shots in the cardinal directions. Also has a chance to spawn a Drowned Charger upon death.
Dukie	288.0	Flies around the room diagonally, occasionally spitting out 1-2 Dart Flies.
Mom's Dead Hand	287.0	Falls from the ceiling. Upon landing, it spawns several rock waves that travel outwards. Spawns several spiders upon death. Entering a room containing Mom's Dead Hand will warn Isaac with Mom's laugh.
Fat Bat	258.0	Slowly flies towards Isaac. Tries to align itself diagonally to Isaac and shoots at him when in that alignment.
Blister	303.0	Slowly hops towards Isaac, occasionally spawning a Dark Ball. Spawns a Sack upon death.
Poison Mind	301.0	Slowly crawls/floats around the room diagonally, leaving a trail of damaging green creep. Explodes upon death.
Mr. Red Maw	35.2	Walks towards Isaac and attacks by launching its head towards him. Turns into a Red Maw or Gusher upon death depending on the killed body segment. Occasionally separates at will.
The Thing	304.0	Crawls along a wall and attempts to line up with Isaac, then spits a line of damaging Red Creep.
Stoney	302.0	Chases Isaac and blocks tears, but does not deal contact damage. Temporarily pauses in exhaustion after a certain amount of time. Invulnerable; dies when the room is cleared.
Cross Stone Shooter	202.10	Stationary and invulnerable monster that continuously fires shots in four directions, alternating between cardinal and ordinal.
Portal	306.0	Spawns various enemies from the current floor until it either vanishes or is killed.
Swarm Spider	884.0	Very erratically hops toward Isaac in large groups, dealing contact damage.
Migraine	869.0	Crawls around the room erratically, following Isaac and dealing contact damage. Can jump small distances. Releases multiple Troll Bombs upon death.
Eggy	29.2	Hops aimlessly around the room, spawning slowing white creep wherever it hops. Spawns a group of Swarm Spiders upon death.
Triple Grimace	42.2	Stationary and invulnerable monster that occasionally fires a triple shot at Isaac. Stops firing when room is cleared.

Degraded Bosses:

Name	ID	Notes
Blastocyst	74.0	Small-form only
Chub	28.0
Dingle	261.0
The Duke of Flies	67.0
Fistula	71.0	Medium-form only
The Haunt	260.0
Headless Horseman	82.0	Only the head
The Hollow	19.1
Larry Jr.	19.0
Mega Fatty	264.0
Monstro	20.0
Pin	62.0
Polycephalus	269.0
Super Greed	50.1
Teratoma	71.1	Small- and medium-form only
Widow	100.0

Bosses


The Adversary	The Bloat	Loki	Mask of Infamy


The Gate	War	The Fallen	Headless Horseman


Brownie	Sisters Vis	The Pile

Double Trouble

Double Trouble Bosses


(Double Trouble) Blighted Ovum	(Double Trouble) The Haunt	(Double Trouble) The Husk	(Double Trouble) Larry Jr.


(Double Trouble) Dangle	(Double Trouble) Little Horn	(Double Trouble) Rag Man

Final Boss

Mom will always appear on the second floor of this chapter or in the last boss room if Curse of the Labyrinth is active.

Mom

Unlockable Achievements

Something Sticky - Beat Chapter 3 20 times.

Leprosy - Beat Chapter 3 without taking damage.

Dark Boy - Beat Chapter 3 without taking damage.

Trivia

A necropolis is a large ancient cemetery with elaborate tomb monuments. In Ancient Greek, νεκρόπολις or nekropolis literally means "city of the dead".
In the original The Binding of Isaac, Daddy Long Legs, Triachnid, Carrion Queen, and The Wretched could appear as bosses.