Interesting situation in the Phillies - Orioles game last night. Top of the 9th, Orioles hit into a 5-4-3 double play. Orioles challenge both outs (at 2nd and at 1st). The ruling was... out at 2nd confirmed, out at 1st overturned. (The runner at 2nd was clearly out, and I initially wondered why they included that one in the challenge.)
The interesting part is that the Orioles retained their challenge... and subsequently used it in the bottom of the 9th. I can't find any online resource for the MLB's challenge rules. How many things can you challenge in one play? Do you only have to be right about one thing to retain your challenge?