Is Garmisch to Fussen/Neuschwanstein possible?

According to RometoRio website it can be done but not too swiflty, via train through Austria or via bus. Sounds like a German western movie starring Gehardt Cooper, The Slow Coach to Fussen.

Yes, there are buses from Garmisch-Partenkirchen to Hohenschwangau (where the Neuschwanstein kiosk is). They run through Oberammergau. You can find these buses on the German Rail query webpage. You can also get from GaP to Hohenschwangau by taking the train to Reutte or Pfronten-Ried (or -Weißbach) and going by bus from there (also shown on the DB page).

The route via Oberammergau or Pfronten would be covered entirely by a Bayern-Ticket. A Werdenfels-Ticket would not cover the entire route - not Echelsbacher Brücke to Hohenschwangau or Pfronten-Ried to Hohenschwangau. The bus via Reutte would not be fully covered because the bus from Reutte to the German border is in Austria.

Take the train from Garmisch to Reutte in Austria (Ausserfernbahn) and transfer there to a bus to Füssen. You can find that connection if you select at the DB website Reutte as an intermediate stop. You can travel on a DB "Regio Werdenfels" ticket for €26 (for two) to Reutte. The bus from Reutte to Füssen is in addition (just a few €). A typical connection for a day trip would be Garmisch dep.9:04, Reutte arr. 10:00, dep. 10:04, Füssen arr. 10:30. / Füssen dep. 17:13 Reutte arr. 17:42, dep. 18:01 Garmisch arr. 18:57.

You might also check with the local tourist office to see if a day trip bus tour leaves for this same destination.

I found the answer by doing this:
From GaPa Hbh take the 9606 bus past Oberamergau to Echelsbacher Brucke. Pay the driver €10 for day pass. Switch to bus 73 to Hohenschwangau. And viola, you're there. 2 hours total.

After touring the castles, we took a bus to Fussen. Not sure what number. Then hopped on a DB train onto Munich for the next leg of our trip.