The brother to the evil semi-sentient sword Stormbringer. This was acquired by Elric's evil cousin Yyrkoon.
Presumably, like Stormbringer, it is able to drink the souls of those it strikes, passing on some of the life force onto its wielder.
In the final battle between Elric, armed with Stormbringer, and Yyrkoon, armed with Mournblade (The Dreaming City), Elric won, so perhaps, Stormbringer is in some way superior.