[MavsObbession]

Hey, there LudiImpact! I'm also preparing for Nats, hope to see you there! Great team, but there is always room for improvement....

The very first thing I notice is that Latios has Hidden Power [Fire]. Latios will lose speed ties to opposing Timid Latios, so I suggest Substitute or Hidden Power [Ground] > Hidden Power [Fire]. Substitute prevents you from being Sucker Punched, (like my boy pokemaster649 said), and HP Ground simply gives you more coverage. Trust me, HP Fire isn't a good choice; there will be times where you have to rely on speed ties against opposing Latias, Latios, and Gengar. Although, you have the option of giving Latios Grass Knot, instead of having to resort to Draco Meteor to take out Gastrodon and opposing Tyranitars. Here are the calcs for Latios:

Gastrodon (Max HP)
Grass Knot: (75.2% - 89.9%)
Draco Meteor: (64.7% - 76.1%)

Tyranitar (Max HP in Sand)
Grass Knot: (44.4% - 53.1%)
Draco Meteor: (38.2% - 45.4%)

As you can see, Grass Knot is more effective, but of course, Draco Meteor should be part of the moveset. I'm just saying Grass Knot is also a good choice over HP fire. A Grass Knot + Dragon Gem Draco Meteor 2HKOs Max HP TTar in Sand.

As for your own Tyranitar, Chople Berry will help survive a CC from Max Attack Hitmontop, but if you find that Chople Berry isn't working for you against other mons, switch it with Focus Sash. But I recommend you keep the Chople Berry, for the time being.

Reflect is OK on Cresselia, just because it ups your defense, but Ice Beam is also a good choice for coverage againist Dragon-types, if Latios and Zapdos are out.

Other than that, your team looks GREAT! You'll do well in Nats!

Hope I helped!