Familiars that follow behind Isaac have a certain priority in how close their position is to him over other familiars, with Mongo Baby having 4th priority.
Despite bearing similarity to previously mentioned familiars, Mongo Baby will not copy the effects of:
Demon Baby: Mongo Baby behaves like Demon Baby, and will no longer shoot its regular tears unless Isaac has another compatible familiar. If Isaac has other familiars that Mongo Baby can mimic, its behavior alternates between Demon Baby’s and the other familiars’.
Lil Loki: Mongo Baby's tears will become red, but Mongo Baby will not fire in four directions.
Trivia
According to Edmund, this item is a bunch of babies cut up and put back together to create the "mongoest" baby.
Mongo Baby shoots once every half second.
Mongo Baby shoots at the same rate as Isaac at base tears, 2.73 tears per second.
This item belongs to the 
Conjoined set. Collecting three items from this set will transform Isaac into a three-faced version of himself.
Cambion Conception or 
Monster Manual.
Demon Baby: Mongo Baby behaves like Demon Baby, and will no longer shoot its regular tears unless Isaac has another compatible familiar. If Isaac has other familiars that Mongo Baby can mimic, its behavior alternates between Demon Baby’s and the other familiars’.
Lil Loki: Mongo Baby's tears will become red, but Mongo Baby will not fire in four directions.
The Binding of Isaac: Rebirth
