The mobile app really needs the grammar tips!.
It really is missing, as 95% mobile user, I am really missing out on the grammar, I can easily do the exercises, but I can't create new sentences because I was taught no grammar besides the ones I see in the sentences I translate.
I am studying French, but I am sure this applies pretty much to all languages.
You can also use Duolingo's web version (www.duolingo.com) in the browser of your mobile phone, when you have rather good Wifi or 4G/LTE and an internet bundle.
I have always both open on my phone, so I can read the grammar Tips and notes in the web version before I do a lesson in the App.