Tried my first key run in Act I on MP2, got five stacks and killed Odeg the Key Warden. He was spawned near the entrance to Fields of Misery, just SE of the lowest spawn point (the WP spawned there). Got a Key of Destruction drop!
Besides the key he dropped 4 rares, 3 ilvl 62 & 1 ilvl 63.
Killed the act 3 keyboss on MP0 and didn't land any keys. (I haven't read the patch notes, maybe you need to be at least MP1 to get a key).
Wow, the MP levels are a significant difficulty boost. My WD could absolutely blow through act 1 runs pre .05, but I just solo'd an a1 run with her on MP1, and it was MUCH harder. Things hit fairly significantly harder, and take a LOT longer to kill than previously.
Tried Act III on MP1 to start, bumped it up to MP2 for a run, then did a few runs on MP3. Xah’Rith is quite a bit harder to kill than the other two so I didn't even try any higher. Found that he's easier to kill if you can fight him in a tight space. That keeps his "illusions" packed in tighter. One key in about six runs so far.