Yes Mother? is a transformation in The Binding of Isaac, added in the Afterbirth DLC.
Obtained by acquiring any 3 items with the mom tag.
Grants a stationary Mom's Knife that trails behind Isaac and deals 2x Isaac's tear damage on contact.
The knife synergizes as the item would.
This page shows the latest information as of the new Repentance+ (Online Co-op) DLC.
To see information about this transformation for the previous Repentance version, check this page instead.