Best counter for Giratina in ultra?

Giratina best coutner giratina!

In all seriousness, i's say probably the steelix, however since you are short on dust, i'd go with the tyranitar for now. Its a pokemon that likely would be powered up to deal with tier5 raids, and is also a powerhouse in masters after incase you want to power it up further, so the investment wont be wasted. Use that for a while, while not the best counter to giratina in the league, it should help to bide time to get the steelix up there.

As a disclaimer, I should say that my opinion is entirely subjective.

That said, I always beat giratina in Ultra league with my DT HS/SE Aggron. Aron is easy to find during this event so it should be easy to find one in the wild you can evolve to 2500ish.

Being low on stardust sucks. Steelix is best for sure. Mines a 98 with 2 charge moves, he's a beast.

If it's running dual dragon. Hands down ninetails. She thanked at least 5 dragon claws without flinching.

Steelix is an incredible powerhouse against giratina in the ultra league. My 2000 CP Steelix DT+C tanks dragon claw like it's nothing. Superb.

I was slightly disappointed by my double legacy Lapras versus giratina.

If you're waiting for a second move for Melmetal I assume you're building up dust? Given the other responses you may want to funnel this into Steelix instead. It maxes out below the CP cap, has massive defense, and a plethora of resistances to build upon it. Make sure you can cover its weaknesses, I've found fire types to be problematic in my PvP scene.