Gwydir (Marin) is alright. There’s loads of obvious off piste on the main climb out of the carpark on the Llanrwst side which is easily lapable.
I’ve heard there’s some stuff in the woods by Cwm too but haven’t been there myself.
The main track that crossed the climb is gone, sadly, but there are new steeper runs – particularly through the wall about 2/3rds of the way up.
And about 6 or 7 great little tracks from the top of the climb (some on TF).
Then there’s the runs the other way from the Sawbench car park (Granny smasher etc. on TF) and the awesome Rugby Club descent, not on TF but in the same direction.
That usually does me for 5 hours or so of riding.
Coed Cwm was awesome when I went in the dry, dunno about this time of year.