Giratina returns as one of the most formidable walls in the game, with its great bulk and unique typing that gives it a plethora of important resistances, as well as being one of the best Pressure users in the game. Unfortunately, it's not all good for Giratina. In fact, if we're being honest, it's mostly bad, although not completely unsalvageable. While he doesn't have a whole lot of weaknesses, the weaknesses he does have are very common in the formats he's usually allowed in. He has to worry about common breakers like Calyrex-Shadow, Marshadow, Arceus-Ghost, Yveltal, Tyranitar, Hydreigon, Urshifu-SS, and the plethora of powerful Dragon-types that roam the most inclusive formats.
He is also forced to rely on Rest as a form of recovery, gaining no other recovery moves, but makes surprisingly good use of it compared to many other Pokemon. Lastly, he does suffer heavily from 4MSS, and he's forced to drop something that's fairly important and he's probably going to miss no matter what set you run. You can't have Rest, Sleep Talk, Defog, a status move, an attacking move, and a phasing move all on the same set.
In all, he's a very hard Pokemon to just slap on any team and he quite often finds himself outclassed by Pokemon like Arceus-Ghost and Lunala, but if you happen to be able to make use of his specific niches (being a Defogger that can check specific opponents like Necrozma-DM and Groudon, while also quite literally pressuring entry hazard setters thanks to, well, Pressure) he can prove to be a very potent defensive Pokemon.
Giratina @ Chesto Berry / Leftovers
Bold - Pressure
248 HP, 252 Defense, 8 Sp. Def
-Will-O-Wisp / Toxic
-Defog / Roar / Dragon Tail
-Rest
-Hex / Sleep Talk
There's a lot of room for customization on this set, but that's not as much of a good thing as it sounds, because no matter what four moves you choose, you'll be leaving some behind that you're going to wish you brought in many encounters. The choice between Will-O-Wisp and Toxic comes down to whether crippling physical powerhouses like Groudon, Landorus, and Necrozma-DM with a burn is more important to you than wearing down bulkier walls with Toxic. It's not entirely unheard of for some sets to utilize both.
Defog is a big part of the reason to use Giratina in the first place, as combined with Pressure it makes him very effective at keeping hazards off the field, especially in match-ups against opposing stall teams. However, you could attempt to run a shuffling set by utilizing RestTalk, a phazing move, and a status move of your choice. When combined with entry hazards such a set can rack up a surprising amount of damage over time, but this set is really a relic of the DPPt days. Defog removing entry hazards, the introduction of Heavy-Duty Boots, and the legion of new Pokemon who can threaten him make it difficult for this set to pull its weight in the current metagame.
Rest keeps him healthy, and is the one move pretty much all sets are going to carry. Pain Split might seem tempting at first but almost never a good idea, being very unreliable thanks to Giratina's gargantuan base HP stat.
Finally, the last slot is again determined by what exactly you want Giratina to do, or rather, what you're prepared to give up it doing. Hex gives you the means to deal some damage, and has overall good coverage (the relatively few Normal or Dark types that Giratina is likely to find itself facing aren't opponents it's going to want to stay in on anyways), but it means you'll be running Rest without Sleep Talk, which can be hazardous without a Chesto Berry. Running Sleep Talk takes up a valuable moveslot and forces you to drop something that you're probably going to sorely miss in some battles, but it significantly enhances his overall staying power and makes him not completely passive after using Rest. Shadow Ball or even Draco Meteor could be carried over Hex if an attacking move is desired; they all have their own advantages and disadvantages.
The EV spread could also be customized depending on what particular threats you plan on checking with him. A simple max HP/max defense spread is hard to go wrong with, though, as most of the things that Giratina is usually used to check are physical attackers.
For teammates, this version of Giratina really only ever works on stall teams. As such, you'll probably want to pair it with other stall staples like Chansey/Blissey, defensive Yveltal, Ferrothorn, and Necrozma-DM.
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