Complex sentence: The remaining League members depart agreeing to continue using their powers for good in the new century, and said witch doctor arrives, performing a ritual that summons an unnatural storm, with a bolt of lightning ambiguously striking the rifle Sawyer left on Quatermain's grave.
Split into simpler sentences: The remaining League members depart agreeing to continue using their powers for good in the new century. Then the witch doctor arrives, performing a ritual that summons an unnatural storm, with a bolt of lightning ambiguously striking the rifle Sawyer left on Quatermain's grave.