Good waterfall run when its up. The first 500m is a rocky grade 2/3, before you reach a series of drops with deep plunge pools. The hardest is probably the last, and you can inspect from the takeout by walking up river right.
From the A4085 turn off at Garreg Llanfrothen and head up to the putin in the village of Croesor. Takeout by the cliffs of Carreg Hyll Drem on the A4085.
Rainchasers is best experienced as an app.