If you have level 100 TRU Arceus and transferred it to Heartgold or Soulsilver you will be able to unlock Sinjoh Ruins. You can only pick 1 among Giratina, Palkia and dialga. Today's pokemon is Level 1 GIratina from Sinjoh Ruins.
Giratina Action Figure
Giratina Action Figure on dry leaves.