This call came up during an event this weekend, and the staff was divided on the proper solution.

Player A casts Path to Exile targeting one of N's creatures, holds priority, then casts Shadow of Doubt. Can player N shuffle their library?

Searching the library is an impossible action due to Shadow of Doubt. However, the staff was divided on whether or not it is legal to say yes to the may part of Path to Exile, fail to search due to it impossible, then completing as many actions as possible (shuffling the library).

Nope, they can't. This is effectively addressed in Gatherer:

If an effect says “You may search your library . . . If you do, shuffle your library,” you can't choose to search since it's impossible, and you won't shuffle.

You only get to shuffle if you choose to search the library. Since the Shadow prevents searching, they cannot choose to try to search. Since they choose not to use the search ability, they won't do anything else listed on the Path, so they will not shuffle the library.

Nathan Long
Wizards.Com Boards NetRep