Card advantage is a strategic concept (rather than a specific game term) and a lot broader, and basically means having more cardboard than my opponents. For starters, any card that puts more cards in your hand is card advantage, even if it doesn't say draw. But card advantage also looks at what happens in other zones
A lot of instant and sorcery cards have cycling as well, making it trivial to boost up Rielle's attack to make it a threat
Probably not, 400 is a lot of cards in a set, and that excludes trainers and full arts and all that chicanery
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Giratina doesn't have a Poke-Power or Poke-Body but it does have two moves, the first move is called Strafe which takes two energy cards, one each of psychic and colorless and does 20 damage and allows you to switch Giratina with one of your benched Pokemon