Transformation help please?

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("fZDBCoAgDIbfxXOXnCheqzfIm0gUdLM69f5li20dDATHvv8bYzGqcRq6VjX3H+Ylr1j2Rz63vdThxYFxIJya+B9AXzPWAmvyqwH0DWMjsCG/GkDfMrYC28e/G59XeuUmwDcBcRN4ZwLPBDETaKdqAH3H2AnsyK8G0PeMvcBepXQB", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [#"Source DB" = _t, #"Source Table" = _t, #"Source Column" = _t, #"Target DB" = _t, #"Target Table" = _t, #"Target Column" = _t]),
    Custom1 = Table.Combine(
                            Table.Group(
                                        Source,
                                        "Source DB",
                                        {
                                         "n",
                                         each let
                                                 a=List.Distinct(
                                                                 List.Split(
                                                                            List.Combine(
                                                                                         Table.ToRows(
                                                                                                      Table.Skip(
                                                                                                                 _,
                                                                                                                 each [Source DB]="" or [Source DB]=null
                                                                                                                )
                                                                                                     )
                                                                                        ),
                                                                            3)
                                                                )
                                              in
                                                 #table(
                                                        Table.ColumnNames(_)&
                                                        List.TransformMany(
                                                                           {1..List.Count(a)-2},
                                                                           each List.LastN(Table.ColumnNames(Source),3),
                                                                           (x,y)=>y&" Hop "&Text.From(x)
                                                                          ),
                                                        {List.Combine(a)}
                                                       )
                                        },
                                        0,
                                        (x,y)=>Byte.From(y=null or y="")
                                       )
                           [n])
in
    Custom1