Peep (ピープ,Pīpu) (also known as Slug Boy, Sluggy, and Pisser from the art booklet of the Unholy Edition) is a boss appearing in The Binding of Isaac and the Rebirth remake. He can be found in The Caves. Dealing with him can be difficult until Isaac get the hang of his patterns.
He appears to be an obese, dark pink-colored humanoid with a flabby body, stubby limbs, bulging round eyes, and a two front buck teeth. He constantly leaves a trail of urine.
Before Peep does an attack, he will give a signal as to what attack he's going to do.
A spray attack that sends ten urine projectiles flying out in a radial burst pattern. This is signaled by Peep smiling and bringing his hands to his face.
A jump that brings him crashing down on the location he last saw the player standing in. This is signaled by Peep smiling and throwing his arms wide.
Oozing out glowing puddles of yellow creep that deal 1 heart damage if Isaac stand in them. These go away after 5–6 seconds, and don't affect characters with flight. This is signaled by Peep frowning and slightly shrinking, along with him making a burping sound.
Additionally, at 66% and 33% health, he'll detach one of his eyeballs and set it to bouncing around the room in diagonal lines. The eyeballs cannot be damaged at all until Isaac kill Peep himself, so don't waste your time shooting. They leave behind a purely cosmetic blood trail but do 1/2 heart of damage on touch normally and 1 if Isaac is fighting him in The Womb. If Isaac happen to run into Peep himself, beware that he always does a full heart of damage on touch.
The following strategies have proven to work against Peep:
The biggest problem in dealing with Peep is the radial burst. Isaac can dodge behind rubble piles (or hover above them if Isaac has flight) to avoid the spray if there are any, but often Isaac will be facing him in an empty room. Isaac's best option there is to stay well away on his left or right side, moving back and forth between opposite sides of the room whenever he launches. At maximum range, Isaac should be able to dodge the burst with just a little movement up or down to put him between shots. Don't forget to watch for the eyeballs, they can sneak up on Isaac if he's focusing on Peep for too long.
Because this fight requires so much dodging, items that require careful aim are best avoided. With good timing, bombs/Mr. Boom can be used to catch Peep when he lands after his jump. Spoon Bender or I The Magician can help greatly in keeping Isaac's shots more or less on target while you dodge the pee spray. Range increasing items will give Isaac more room to maneuver; conversely, range reducing pickups like Number One or My Reflection will make his life harder in this fight. Continuous, sustained fire from maximum range is the order of the day here. Peep's eyes are also slowed down by Skatole, making them easier to dodge.
The Spider's Bite's slowing tears effect affect Peep in an unusual way. While slowed, Peep's jump will send him straight up into the air, then right back to where he launched from (as opposed to Peep launching and then landing at the location he last saw the player). This makes his pattern very predictable, as Peep can be kept at one spot indefinitely, with the player only occasionally needing to move to dodge the pee spray and eyeballs.
Despite being able to jump to great heights, he can't move over rocks while airborne. This allows Isaac to take cover behind or over rocks, but it can also mean that predicting where Peep lands can be tricky without following the urine trail he leaves while he's airborne.
During his death animation, he start "bawling" while flailing his stubby limbs side to side and then stops just before he bursts.
If II The High Priestess reduces Peep's health below 33% health before his first eye comes loose, only one will be spawned. Graphically, he will have both eyes missing, but Isaac will only have to dodge one for the remainder of the encounter.
Both of his eyes are out right from the beginning of the fight. Otherwise, he behaves the same as the original version.
Is physically smaller and behaves like the original, but constantly leaves a urine-trail, even while in mid-air during a jump, which hurts the player if stepped on.
Peep now has 6 eyes, each eye comes out every time he loses 1/7 of his maximum HP. Note that his eyes are no longer invulnerable and can be destroyed.
Peep appears in the demo from the original game.
Peep has the second highest amount of HP among all bosses in Caves and Catacombs (the highest being Gurdy). Some of Peep's appearances from the artbook are very different to his in-game appearance. Three examples:
He was originally going to have six stubby limbs instead of just four.
From the right side of the page, he is also going to possess a slug-like tail.
Also on page 10, at the top left where he was called as "Sluggy", his appearance look very different comparing to the non-playable character Beggar.
He's referred to as "Slug Boy" and "Pisser" in the official art book.
His name is pronounced Pee-pee as a double entendre, for his two sources of damage are urine and his eyes.
Peep's bulging eyes are a reference to Exophthalmos, a disease that causes the person's (including animals) eyes to bulge.
In the original game, if his eye kills Isaac, a Boom Fly will appear on Isaac's Last Will. This is due to the fact that his eyeballs share the same AI as a Boom Fly.
If his urine trail kills Isaac from the original game, a Brain will appear on Isaac's last will.
This is the case with all forms of creep.
The two invincible eyeballs that detach from Peep may be a reference to Gleeok from The Legend of Zelda, a boss which would spawn two invincible heads when damaged.
If one look closely at Peep's death animation from the original game, one can see that Peep is crying blood.
Since Peep's eyes share coding with the Boom Fly, his eyes may explode when Peep dies or even sometimes shoot six blood projectiles in the same manner of a Red Boom Fly and their movement will be slowed by Skatole.
If the character stand right in front of the boss door he will sometimes push them out of the boss room if he jumps on them.