- Meet Professor Juniper in town after earning all eight Unova Badges.
- Talk to the man in the Castelia City Pokemon Center after the player has outsider Pokémon with at least 50 different original Trainers.
Just to elaborate on Question 2:
When you have 50+ Pokemon in your games from other trainers, talk to the guy on the second floor of Castelia City's Pokemon Center on the left-hand side. He is wearing a black suit with shades.
So just get 50 different Pokemon from 50 different people through trade. GTS, Infrared, Wi-Fi, anything. They can all be Patrats or whatever, just make sure they have different trainers. GTS can be a big help.
(Note: you only get one from each person.)
Source: Bulbapedia/ Masteball Locations