Caligo is ranni. Why did she become a dragon? To save her tarnished heolstor from transforming into Bayle after the dlc(read his descriptions) she infused herself with the draconic essence sacrificing her godhood which was later consumed by recluse's baby losing control of her dear consort but refusing to fully leave it all behind. This transformation also stripped the darkmoon greatsword of its darkmoon enhancement leaving a simple moonlight greatsword which is why it looks different and why we cant get the dmgs in nightreign