You can take your time and build both Pokmon as described or, against aggro decks, you can focus all the energy accumulation on Giratina, to retaliate as quickly as possible
Kain, Traitorous Dragoon I dont know that Kain, Traitorous Dragoon is good, per se
Most of the best candidates in my mind are individual creatures which convert accumulated resources (be they cards, treasures, or creatures in play) into direct damage to players
You also don't want to get too far in the hole or Burn can take you apart with topdecks
If you roll chaos you get a 1/1 deathtouching, hasty assassin
Attack 1:[1RR] Explosive Fire (130+) If this Pokmon has any damage counters on it, this attack does 100 more damage