flower or shrub border
Backyard ends at base of hill. About 5 feet in from bottom of hill I have a perimeter drain. I want to create something interesting along the back behind the perimeter drain.
If that area stays moist, this article may help you: https://www.gardeningknowhow.com/ornamental/water-plants/wgen/water-tolerant-plants.htm
If not, then you'll have to decide whether you want a good ground cover or ornamental grass or flowers, and go from there.
If it stays pretty dry due to the drain, this article may help you: https://www.gardeningknowhow.com/special/xeriscape/drought-tolerant-plants-for-nearly-any-landscape.htm