Many shrubs will grow in dense shade, as well as in clay, in zone 5. Some of them may be familiar, and some are quite lovely, unusual plants.

Try looking up a few of these for their sizes and shapes. Some of them can be pruned if their mature size is larger than you want. Keep in mind that most mature sizes listed in descriptions are 10 years or more.

Itea virginica = Summersweet
Hydrangea quercifolia = Oakleaf Hydrangea
Lonicera fragrantissima = Winter Honeysuckle
Euonymus fortunei = Wintercreeper
Taxus x media = Yew
Cornus sericea = Red-twig Dogwood
Arctostaphylos uva-ursi = Bearberry
Berberis thunbergii = Barberry

My experience with oakleaf hydrangea is that they need moist soil, not usually found under trees. As always your experience may vary. Other than that I second stokesjl's helpful suggestions.

I am a plant sadist. So I grow some corkscrew willow in the dry shade. Be careful that this corner is no where near your water or drain, unless you own the rotorooter franchise. (Mine are 60 feet from my water and I have a french drain in between.) I have to prune once a year in jan or feb to keep them from turning into trees. But I use the shoots for decoration---just put them in a vase without water. The florist charges you for those corkscrew stems. My stand of willows has character all winter and green all summer. (I started this stand by buying the centerpiece at a charity auction and putting it in a vase with water. They rooted and I planted their children.)

I'd also try japanese maples. You won't get the brilliant expression of the colors of the cultivars. But you will get plenty. There are hundreds of Japanese maple cultivars. I do not know which are hardy to zone 5. I am currently fond of the coral bark maples---Sangu Kaku (I have 3) and Beni Kawa (I have none yet). Red stems all winter. Beautiful color in the fall--bright yellow on bright red stems.

Five leafed aralia. verigated small thorns. can take all sorts of dry shade.

I believe that all sorts of hollies would prosper under those circumstances. I have a verigated english holly slowly growing in the shade of 2 large trees. It gets no sun between spring and fall. It is a little thin.