B. Licker (fully known as Butt Licker) is a enemy added in the Wrath of the Lamb DLC for the original game. It is commonly found in the Catacombs and less commonly in Utero and Necropolis. They are initially chained up to multiple segments - up to five - similarly to Larry Jr..
The letter "B" actually stands for "Butt".
B. Lickers are very fast and have moderate health, taking about five or six normal tears to die for each segment. They don't follow Isaac and move randomly around the room, much like Larry Jr. They will also destroy Poop if they run into them, and are often spawned in rooms with a lot of Corn Poop, forcing you to deal with Guardian Flies as well.
However, once one of the segments is dead, the others will separate. Therefore when facing multiple chains of them, it is advisable to take them out group by group so you don't end up having plenty of B. Lickers swarming around in the room separately.
They can be defeated easily while still linked if you have an item that provides explosive shots, such as Dr Fetus/Epic Fetus or simply just spare Bombs. Piercing items, such as Technology or Cupid's Arrow also work well. Because they're fast, but can only move on the ground, items that grant Flight are also useful.
- If spawned in a one square area (i.e. blocked by Pits, Poop, and/or Rocks), they will be trapped and only the head segment will spawn, making them much easier to kill.
- Because of their random movements, it is possible for them to run into Fireplaces and take damage. They will also detonate TNT Barrels if they run into one.
- The name B. Licker was originally created as unofficial name, and made official in version 1.4, when the updated credits roll was added. It shares this trait with Mulliboom.
- B. Licker could be a reference to the horror movie The Human Centipede.
- If you kill one of two Lickers that are connected, the blood splash will still appear, but the B. Licker will still be alive. This happens because a 3rd B. Licker is hidden inside of another. This also happens with Larry Jr. in Challenge Rooms.
- B. Lickers will go off screen on rare occasions. This will end your run, unless you can use a Bomb to get out of the room.