Mynnydd Meandy, or Old Bill Descent is pretty good, some rough going but its pretty fast in sections.
If you’re looking at an OS, go east from that BW above and look at the path Twyn Crugyrafan that goes down around the edge of the basin and down into Cwmparc, thats a pretty impressive alpine type descent. Plus the one just north of that, Cwm Saerbren/Treherbert Basin, brutal bike/body wrecker but well worth doing.
The other bridelway into Blaencwm is awesome too, try and get past all the rocks without dabbing.
Theyre all on Strava too if you want links.