One of the most striking features about Giratina-O is its unique typing. Ghost/Dragon with Levitate provides it with six resistances and three immunities, including important resistances to Water,
Electric, Fire, Bug, and Grass, and immunities to Normal, Fighting, and Ground. In addition, its typing grants it fantastic STABs, hitting most of the Pokemon in the Dragon and Psychic-infested Uber metagame for super effective damage.
Base stat wise, Giratina-O possesses an interesting balance between offense and defense. With 150/100/100 HP and defenses, Giratina-O is well-suited to take on resisted but powerful hits (with the exception of Water Spout from Kyogre). Short of a Draco Meteor from Dragons, Giratina-O is incredibly difficult to OHKO. On the offensive side of things, Giratina-O can utilize its great base 120 Attack and Special Attack very well due to its amazing STABs and access to powerful attacks such as Draco Meteor and Outrage. While 90 base Speed is somewhat slow by Uber metagame standards, a fair amount of Pokemon that share the same base Speed often prefer to invest in bulk, such as Groudon and bulky Kyogre. Since Giratina-O is an offensively-minded Pokemon, it will often have Speed EVs invested, allowing it to outrun a small but crucial portion of the Uber metagame. With access to Shadow Sneak, Giratina-O can somewhat bypass its average base Speed and revenge kill weakened foes.
Speaking of moves, Giratina-O packs a wide variety of offensive options. On the physical side of things, it learns the key moves Outrage, Dragon Claw, Shadow Sneak, and Earthquake, with each having unique roles. Its special movepool is slightly larger, as it learns Draco Meteor, Dragon Pulse, Shadow Ball, Aura Sphere, and Thunder, and these can be amplified by Calm Mind. Although Giratina-O wishes that it could learn Flamethrower or Fire Blast like its fellow Dragons, Hidden Power Fire will suffice for taking care of Scizor and Forretress.