Osmunda regalis, Royal Fern. Here is a link that might be useful: Royal Fern

Part of my streambank is like yours; almost vertical. I'm assuming the stream can rise during rains. Xanthorrhiza simplicissima and Leucothoe are good, low-growing (native)colonial shrubs which will stabilize the bank. Vinca minor and V. major should also work, as might Lamium. Chrysogonum virginianum 'Eco Lacquered Sunset'and Ajuga spread vigorously in shade. A few of the low-growing bamboos will spread slowly in deep shade, but beware of their aggressiveness if they find a brighter area. Plants competing with tree roots will need supplemental water for a few years until established. That means watering several hours a week with an oscillating sprinkler. I think adding soil or making terraces would be a waste. Lessening the tree cover would certainly help your ground covering plants grow.

Stahlmaster, your little creek is beautiful. I think Cotoneaster would look great draping over your bank. We have a dry creek running through our property but ours is dry most of the year. We have large trees with exposed roots which we don't want to damage. Since we've cleared out some of the under growth we now have ferns there. Some other things I want to try are Galtheria procumbens (winterberry), Galex urceolata, Sweet flag, Iris ensata, and cornus canadensis if I can find it. Doing research on things that won't take over. No ivy or Chameleon plant!!!! Good luck. Would love to hear what you decide to plant.

Tradescantia fluminensis ?