After you beat Sabrina on Pokemon Leaf green and Fire red
it rises Pokemon's status
Battle Tower
you get it after you beat Sabrina
mosdeep gym or from gardevoir
Level 33
After beating Mosdeep City Gym.
Trade in Battle Points at the Battle Frontier(48BP)
level 35. gardevoir's best function is as a calm mind spec. sweeper, in my opinion
namely pchycihich type poekmon and those that have high special attack of over 100
Return if its really happy with you, and calm mind if it doesn't like you. Return, because with calm mind you waste a turn and you don't do anything.
Raikou because its got some powerful Electric moves like Thunder, Crunch and Calm Mind
Celebi @ Leftovers Nature: Timid/Modest Calm Mind Psychic Leech Seed Heal Bell No need for recover