Peeping
Peeping is a boss that can appear in 
Utero. It is the giant boss version of 
Peepling.
Behavior
Peeping spawns in the center of the room, resembling a giant blinking 
Eye, before ripping itself out of its socket in the ground and beginning the battle.
Peeping has 3 separate phases, with 425 HP shared between its first two phases.
Phase 1
During the first phase, Peeping will perform the following attacks:
- Inflates a large
Haemolacria tear, floating a short distance diagonally while doing so. After the tear is fully inflated Peeping will pause in place for a moment before lobbing it. Upon impact, the tear will pop into 8 smaller projectiles in a ring that are arced high above the ground. Each of the 8 projectiles will then burst into more 4 projectiles, with the ones closest to the cardinal directions releasing them in the ordinal directions, and vice versa.
- Peeping has somewhat delayed aiming, launching the blood tear towards Isaac's location right after inflating it, rather than where he is at the moment its fired.
- A safe zone is created in the center of the attack after the first projectile lands, as the 8 shots pass over Isaac and the following projectiles create a ring around the center.
- Peeping quickly creates a ring of projectiles around it that remain in place, similar to Peepling, during which it will float rapidly to align itself a set distance away from Isaac in the closest cardinal direction. After a short pause, Peeping will fire all the projectiles outwards, with 5 of the projectiles along the cardinal direction closest to Isaac traveling much faster than the others.
- Peeping roars and travels to the center of the room. After a brief delay, Peeping will fire a
Brimstone beam which rotates to follow Isaac's movements. It then pauses a moment before, firing a second Brimstone beam ahead of Isaac to try and cut him off.
- Both the speed of Peeping's rotation and the speed of which this attack is performed scales with Isaac's movement speed.
Phase 2
Once brought below 75% of its HP, Peeping will slam a tentacle into the ground and summon 4 invulnerable Peepstalks in the quadrants of the room before hurling an eyeball into each one.
Peeping has the same attacks as the first phase, but with all 4 Peepstalks performing additional attacks during each:
- As soon as Peeping inflates a Haemolacria tear or releases a ring of projectiles, all Peepstalks will launch a large blood tear roughly towards Isaac's location in unison, which leaves a small pool of red creep on impact.
- These tears aren't aimed at Isaac, but rather a set distance diagonally from Isaac's position in all 4 ordinal directions, forming a square around him.
- When Peeping roars, each Peepstalk will aim a faint yellow indicator beam at Isaac's location. After Peeping reaches the center of the room, each Peepstalk fires a Brimstone beam in the direction of the indicators. Peeping will proceed with its Brimstone attack after the beams fired by the Peepstalks disappear.
Phase 3
Once Peeping's HP drops to 100, it will begin to rip out its eye from its body, launching it high into the air and causing all Peepstalks to collapse and turn into Peepees. Afterwards, Peeping's body will die, leaving its eye, which now starts with 150 HP.
- While ripping out its eye, Peeping can be damaged, but will not fall below 25 HP.
Peeping's eye will continuously roll in a steep diagonal pattern, bouncing off walls as it does so. Each bounce against the top or bottom walls of the room will release a large ring of blood projectiles, made up of an alternating pattern of 8 singular projectiles and 8 short diagonal lines of 2 projectiles.
- Peeping will only fire projectiles if a sufficient amount of time has passed since last performing the attack, to prevent Peeping from firing too often when reaching the ends of a room. Due to its rolling angle, Peeping will very rarely fire projectiles from impacting the left or right walls.
- Peeping takes 3.5 damage from recoil every time it hits a wall, down to a minimum of 10 HP, after which it no longer hurts itself.
- Peeping's rolling speed depends on the amount of Peepees alive, reaching its maximum speed if there are none left.
If there are any Peepees alive after Peeping's eye has been killed, they will remain alive and have to be killed to finish the fight.
Notes
- Peeping can still be damaged during the transition to Phase 2; if Peeping reaches its Phase 3 threshold before it can launch eyes into waiting Peepstalks, then the Peepstalks will remain without an eye when Peeping transitions into Phase 3, and it will also not collapse or turn into a Peepee. Instead, it remains stationary for the rest of the fight and will only disappear once the room is left.
- Peeping will also completely skip the phase 2 transition if he is killed quickly enough, resulting in no Peepstalks spawned at all.
Spawns
Peepstalks
Peepstalks are invulnerable enemies spawned exclusively in the second phase of Peeping's fight. They spawn as a group of 4 in the four quadrants of the room and will remain stationary as they assist Peeping in the fight by adding additional effects on top of its attacks. When Peeping reaches its third phase all Peepstalks crumble and turn into Peepees.
Notes
- Peepstalks can be destroyed by
Euthanasia and 
Little Horn tears. They will also not turn into Peepees if killed.
Peepee
Peepees are usually only encountered in the third phase of Peeping's fight, but can be rarely encountered in regular rooms. They will hop 3 times in random directions before firing a large blood projectile towards Isaac and then repeating the pattern. They have fairly low friction, sliding around when hopping, and take a fair bit more knockback from damage.
Video Showcase
Trivia
- Peeping originated from an old mod called The Peeping, one of the very first boss mods to be created for The Binding of Isaac: Afterbirth+.
Gallery
Peeping while in the ground.
Peeping roaring.
Peeping in its third phase.
Appearance of a Peepstalk without an eye.
Drawing of Peeping in the Bestiary and on Isaac's last will.
Peeping's health bar icon if Enhanced Boss Bars is installed.
Peeping's Enhanced Boss Bars icon in its third phase.
Peeping as it appeared in the standalone MOD for Afterbirth+.
 Bosses 
| |
|---|---|
| Chapter 1 | Buck - Honeydrop - The Whispers - Griddle Horn - Buster - Meltdown |
| Chapter 1.5 | Ghostbuster - Cacamancer |
| Chapter 2 | Battie - Kingpin - Slinger - Monsoon - Aquagob |
| Chapter 3 | The Organization - Gutso the Great - Luncheon - Pollution - Tsar - Junkstrap |
| Chapter 3.5 | Warp Zone - Dusk - Madomme |
| Chapter 4 | Basco - The Sun - Peeping - Cacophobia |
| Chapter 4.5 | Mr. Dead |
| Minibosses | Psion - Gravedigger - Hermit |
| Vanilla Boss Champions | Golden Plum - Ghost Larry Jr. - Mucus Monstro - Technopin - Albino Widow - Beehive Fistula - Possessed Hollow - Wine Husk - Kidney of Infamy - Alien Loki - Fiend Mom - Alien Lokii - Grinch Krampus |