Complex sentence: Later Enlil disguised himself as the "man of the boat", impregnating her with a fourth deity Enbilulu, god of rivers and canals, these act as substitutes for Nanna/Suen to ascend.
Split into simpler sentences: Later Enlil disguised himself as the "man of the boat", impregnating her with a fourth deity Enbilulu, god of rivers and canals. All of these act as substitutes for Nanna/Suen to ascend.