Get the soul of either curly or devil or manticore. If you already have these souls apply one of these and use it to get to the other side of the waterfall

and one more thing, you can get the claimh solaisunder the boat the area with those skulls that breathe out something. get past them and start slashing at the wall until it breaks down. The claimh solais is the most wonderful weapon for me than the final sowrd

use curly soul

first u must have the soul dat u walk ontop of the water n the soul curly or mantiroce or
devil

use sliding dash