From publisher blurb:
"That Boss" Your Group is Sure to Remember
A "That Boss" is a new type of boss fight that will challenge players in a way that few published products ever have. Drawing influence from phased boss fights, prioritizing actions that aren't just "I try to do damage", and forcing dynamic movement from characters are just some of the things that a "That Boss" offers.
Our Lady of the Depths is a deific statue of a woman that radiates a magical but corrupting essence. Enthralled worshippers willingly undergo a metamorphosis to better serve her and her isolated "cult" will do whatever it takes to spread the good word.
Our Lady of the Depths can be inserted into nearly any fantasy setting as a little known secret from a bygone age, an incredibly popular rumor, or a well-known place that is oft avoided by the sensible. Build an entire adventure around this battle or find a way to refluff it an insert it into nearly any adventure!