Once known as the King of the Ultra League, the Renegade Pokémon keeps excerting its pressure among the GBL meta! Giratina-Altered has massive defensive stats and a great typing. Both of its Fast Moves are viable, so chose according to your team's needs: Shadow Claw turns Giratina into a spammy generalist only walled by Normal and Dark types, while Dragon Breath flips the matchups against the last two at the cost of now struggling against Steel types. But the biggest Giratina counters are the Fairy types, so be sure to pair it with Steel or Fire types that can take care of those!
If you are hunting the Rank 1 possible for Giratina-Altered, you have to trade with someone you are only Good Friends with & hope for a 1/12/15.
Alternately, you can trade with a Best Friend for hopes of a 5/12/13
There's also a case to be made for Raid IVs and if you go that route find a 11/15/13
Partners & Threats
When running Giratina-Altered in the Ultra League, we suggest pairing it with at least one of the following: Registeel, Charizard & Melmetal.
You must be wary of Charmers (Clefable & Togekiss), Articuno & Cresselia no matter the move set you are running. Other threats are Scizor, Alolan Muk & Lapras though Giratina may be able to win in certain shield situations & move set changes.
We always like to help you answer a few questions when building a Pokemon to use in any league so, should you?
Should I Trade? Yes, we suggest trading for better PVP IVs.
Should I Best Buddy? For Ultra League, Best Buddy Giratina isn't neccesary & those resources would be better used elsewhere.
Should I Elite TM? NO, Giratina has no legacy moves currently & this would be a waste of a very valuable item.