In reply to Jim Houghton:
I don't think it's that bad! There are fewer buses than there used to be, but they still run and it would be great to have people using them more! Buses from Bangor Station to Llanberis and back run through the day (although not early and late, and require a bit of planning to avoid waiting). Nos. 85/86 ( https://www.gwynedd.llyw.cymru/en/Residents/Parking-roads-and-travel/Bus-ti... ).
The S2 Sherpa runs 5 times a day from Llanberis, via Pen y Pass to Betws y Coed at reasonably convenient times (also in link above). Harder to get round to Ogwen, but some good routes on the Glyderau from the S2 route. Taxis are generally pretty available, but can be expensive.
There are other bus routes which might be useful, towards Beddgelert, etc.
I think it would be fine to do a trip combining train, bus and taxis where required.
I find the buses pretty reliable in general, although driver sickness might affect this at the moment.
Feel free to DM if you need any more details. It would be great to have more people coming on public transport!
Post edited at 08:07