Giratina is arguably one of the best physical walls in the game. With colossal base 150 HP and massive base 120 Defense, Giratina can easily wall some of the most dangerous threats in Ubers, such as Groudon, Metagross, Scizor, and Ho-Oh, with little effort.
Earthquake allows Giratina to handle Taunt Heatran, which otherwise dominates most sun stall variants.
Will-O-Wisp cuts Giratina's enemies' Attack stats to pieces, rendering them incapable of hurting this great wall, as well as biding time for Giratina to use Rest to restore all of its HP, thus becoming ready to take on the next opponent it faces. Sleep Talk enables Giratina to absorb status and ensures that it isn't set up bait for Rayquaza and Arceus, seeing as Sleep Talk may pick Will-O-Wisp and ruin their fun. Roar also allows Giratina to act as a good phazer and can be used over Will-O-Wisp if your team relies heavily on Toxic Spikes, because then Giratina could not burn as many opponents. Giratina also has a distinction as being one of the few spinblockers that can phaze. Dragon Claw enables Giratina to severely damage other Dragon-types, OHKO Deoxys-A, and deal a respectable amount of damage to Ho-Oh and Darkrai; whereas Dragon Pulse carries a dash more power against Groudon.
Many of the powerful special attackers in Ubers will quickly decimate Giratina with their powerful strikes. It doesn't help that Giratina possesses weaknesses to Dragon-, Ice-, Ghost-, and Dark-type attacks, all of which are commonly used attack types in the tier. Mewtwo and Darkrai can both make Giratina useless with Taunt and then proceed to set up quickly and wipe Giratina away with powerful super effective special attacks. Many of the powerful Dragon-typed special attackers, such as Dialga, Palkia, Giratina-O, Latios, and Latias, will easily steamroll Giratina with STAB Dragon-type moves; though the last two will not want to eat Giratina's STAB Dragon Claw. Kyogre can easily pick off Giratina with Ice Beam or sometimes Water Spout, should Giratina be weakened, or set up on it with Calm Mind. Finally, there a few physical sweepers that will easily KO Giratina, such as Rayquaza (after it sets up), Choice Band Garchomp, and Bulk Up Dialga; although the former two will hate Will-O-Wisp. Steel-types make great teammates for Giratina, as they resist all of Giratina's weaknesses, and can beat many of its common counters.
Specially Defensive Scizor is a superb example of a good teammate. It can easily switch in on Mewtwo (beware of Flamethrower), Darkrai (watch out for +2 Focus Blast), Latias, and Latios (watch for Hidden Power Fire), and OHKO them all with U-turn, trap them with Pursuit, or pick them off with Bullet Punch. Thanks to Scizor's Dragon-type resistance, it can easily switch on Dialga's, Palkia's, Giratina-O's, Garchomp, and Rayquaza's Dragon-type attacks as well, provided they aren't holding a Choice item that boosts attack power. (If they're not holding a Choice item or locked into Outrage, do not switch into them or you will likely get roasted.) Another good partner for Giratina is Jirachi, since it can take any Dragon- or Ice-type attacks aimed at Giratina and can cripple threats such as Calm Mind Mewtwo, Calm Mind Kyogre, Latias, and Latios with Toxic, hampering their ability to set up on Giratina effectively. It can also stall out non-Choice Specs Kyogre and Palkia with a combination of Wish, Protect, and Toxic, and, like Scizor, Jirachi can revenge kill Garchomp and Rayquaza locked into Outrage. Jirachi can also enhance Giratina's ability to take hits with Wish, Reflect, and / or Light Screen.
Blissey can take any special attack thrown at Giratina and use Wish to help ease Giratina switching in to battle or Aromatherapy to cure Giratina's self-induced Sleep status. Forretress also resists all of Giratina's weaknesses and can easily switch to set up entry hazards, which will greatly hinder the opposing team. Giratina also blocks Rapid Spin, so you will not lose your entry hazards. A supporting Dialga can deal with non-Choice Specs Kyogre and can cripple Mewtwo, Latias, Latios, and other special attackers by using Thunder Wave. Additionally, a Calm Mind Latias of your own, despite sharing Giratina's weaknesses, can take on most Kyogre variants, Giratina-O if it does not have Stealth Rock damage, mixed Dialga, and Palkia. Be careful though, as Latias is 2HKOed by Choice Specs Kyogre's Ice Beam. Groudon also gets a mention, as it can deal with the physical attackers that Giratina cannot, thanks to its high Defense, lack of a Dragon weakness, and Dragon Claw as well as access to Thunder Wave to cripple fast sweepers.
Giratina walls physical attackers, such as Groudon, Scizor, Metagross, Heracross, some Tyranitar, and physical versions of Ho-Oh almost effortlessly, so sweepers who normally have trouble with these threats make good offensive teammates for Giratina. Pokemon such as Mewtwo, Darkrai, Latios, Latias, Shaymin-S, and Deoxys-A all benefit from having Giratina around to incapacitate these threats, as they can all block sweeping attempts made by any of these Pokemon. Rayquaza is also an excellent complement, as Groudon (watch out for Thunder Wave), Scizor, and Metagross can no longer stop Rayquaza from sweeping once they have their Attack cut by Will-O-Wisp. Garchomp works the same way as Rayquaza.