Foetus
Foetus are variants of 
Homunculi that appear in Corpse and behave similarly. They spawn tethered to obstacles and walls, like their counterparts, but will break away much quicker and move slightly slower after being freed. When Foetus escape from being tethered, they will release a ring of 8 blood projectiles from the point where they were tethered and pull out a Foetu ― and, if the Foetus was tethered to a rock, will destroy it in the process.
Foetus, after being released, will continue to relentlessly chase Isaac while dragging a Foetu with it, the pair behaving similarly to 
Gemini.
If Foetus is killed while still tethered to the wall, or if the obstacle Foetus is connected to is destroyed before they untether themselves, then no Foetu is spawned. If the Foetu is killed first after spawning, Foetus will continue to chase Isaac with no change in behavior.
Foetu
Foetu are pulled out of walls and obstacles by Foetus. Foetu will float in place while being dragged by Foetus by their cord, occasionally shooting a spider ball towards Isaac. These spider ball projectiles can be damaged and will split into 2 
Spiders on impact or when destroyed. It will not fire any more projectiles if there are 4 or more Spiders currently alive.
If their tethered Foetus is killed, Foetu will become enraged and chase after Isaac wildly around the room, similar to Suture when Contusion is dead. In this state, Foetu receives heavier knockback.
Foetus are most commonly spawned by Foetus, but can rarely appear in a few rooms on their own, where they will always be in their enraged state.
Trivia
- In the same way that Contusion and Suture are referred to collectively as Gemini. Foetus and Foetu are named "Siblings".
- The names Foetus and Foetu may be in reference to the concept of "fetus in fetu", where a malformed fetus is fully enclosed in the body of its twin.
- Foetus and Foetu's names use the British English spellings of the words Fetus and Fetu respectively.
- The only other enemies in the MOD that share this property are
Haemo and 
Armoured Looker.
- The only other enemies in the MOD that share this property are
- Foetus and Foetu were originally from the unreleased Morbus MOD.
Gallery
A detached Foetus.
A Foetu's appearance spitting out spiders.
An angry Foetu.
