No reason you can't go DOWN the North Rib as well. The North Rib has more class 3 climbing - a lot of it can be on slabs. The other routes down the back side of Tyndall (like the Northwest Ridge) include a lot of bouldering on loose boulders, but it is more class 2. Route finding on the Northwest Ridge can be tricky and can lead you to exposed, class 4 obstacles. There is no definite "trail" to follow on any of the routes.