5 Oct 2018
You may target zero cards in your graveyard and still shuffle your library.
5 Oct 2018
A spell that can't be countered is a legal target for Devious Cover-Up. The spell won't be countered when Devious Cover-Up resolves, but you'll still shuffle cards into your library.
5 Oct 2018
Devious Cover-Up can't target itself at all. You can't try to counter it with itself and shuffle cards in, and you can't use its effect to shuffle itself into your library.