The Skull Splitter is an Operator Mod featured in Call of Duty: Black Ops 4. It is only available for the Mozu and ensures that every headshot with the Mozu is lethal.
In Zombies mode, the attachment gives the Mozu a significant headshot damage boost, being able to kill with a single headshot from an un-Pack-a-Punched Mozu up to Round 24. This effect gets stronger with every Pack-a-Punch. The damage effect is mitigated by Water Catalyst buffs.