Search for your desired item or category. For example, "phone cases"
Select the url on the search results page and paste in: &pct-off=20-50
You can change the numbers to alter what % discounted items you want to see. For example, "&pct-off=40-70” would show you items with a 40-70% discount, whereas "&pct-off=20-50” would show you items with a 20-50% discount