Leviathan is a transformation in The Binding of Isaac, added in the Afterbirth DLC.
Obtained by acquiring any 3 items with the devil tag.
+2 Black Hearts.
Grants flight.
Can be obtained as a rare reward from Sanguine Bond.
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.