Pretty much continuous grade 2 with some 3. Keep your eyes out for possible tree/fence portages. Hop out at the A470 bridge as the difficulty ups a little and it's worth inspecting the next 500m for trees. Down to the viaduct there's some slides, a slot then a sweet double drop into a slot rapid into a clean 4ft drop. Get out at the viaduct as there's sumps and nastiness if you choose to continue.
Takeout at the viaduct just after the A470 roadbridge (just south of Ffestiniog). A footpath river left leads back to the road. To reach the put-in, head upstream along the road on river right to Cwm Farm.
Rainchasers is best experienced as an app.