Separate units for strong, weak, and mixed inflection?
I realize how hard it must be to pick just the right examples covering only the material covered thus far, without being redundant or boring. On the other hand, declension is one of the more challenging bits of learning German it seems. For this reason, I think this topic needs some separate handling. (Sorry, not meaning to create MORE work for Duolingo folks; I do see this as necessary.)
Maybe break up declension into individual units for each of strong, weak, and mixed, perhaps having more than 1 of each if you deem it necessary. Perhaps sprinkle these through the other units so as to avoid bombardment of these different declensions which could easily become confused and mixed up. Let the student (me?) become familiar with each, while proceeding on to learn other concepts, Duolingo style.
Again, just injecting suggestions for making the language a bit easier to master. I understand that every one of these ideas means more work for the people who support this platform, and that is greatly appreciated.