Was messing around with the unmount dash more and found a extremely consistent way to get it.

After the initial press and release of mount + hunter dash IMMEDIATELY start to hold both buttons again then release them roughly 3-5 frames after the smoke cloud appears for the mount.

The timing seems to effect the distance traveled not slopes (although terrain could play a part in it), getting the unmount dash on the last possible frame seems to be why you get a massive boost sometimes.

Now the window for this is still extremely strict and hard to get 10/10 times but the best way of practicing this for me was to use the motorcycle mount Napdragon Cruiser (for the clearer sound effects) and go to the beach to the right of Drakesnout Range.

Found a weird movement tech with the mount. This was done on the latest patch on the switch version.

After testing more you can get this semi-consistently by pressing the hunter dash and the mount at the same time twice while the weapon is out and get insane distance at times.