Right, so there are a couple elements of this team that need work. Your massive Ice weakness is one, and you have really nothing outside of Volcarona to actually check Ice-types. This team also struggles with bulky Waters, Landorus-T and Mamoswine. After plugging your team into Team Magma, you have a massive problem with Fighting, Rock, Ice and Water. All new additions will be in bold (I warn you, I made a lot of changes).
Old Team:
Tyranitar / Volcarona / Landorus / Salamence / Klefki / Milotic
New Team:
Tyranitar / Cradily / Landorus / Charizard / Aegislash / Milotic
Tyranitar
Tyranitar@ Tyranitarite
Sand Stream | Jolly
100 HP / 220 Atk / 4 Def / 4 SpD / 180 Spe
- Crunch
- Rock Slide
- Dragon Dance
- Protect
I can't find it in my heart to remove Tyranitar, despite his 4x Fighting weakness, so we'll fix the team around him. Nothing changes; I've seen D-Dance Tyranitar first-hand, and it worked marvellously (until it got defeated by another Tyranitar, but that's beside the point). A good place to start.
Volcarona
Due to an addition made later, Volcarona needs the boot. He compliments T-Tar well and allows for setup with Rage Powder, but he should also be able to attack when needed. I would advise either getting a new Rage Powder user or one that can hold up in the Sand and still support Tyranitar.
Cradily@ Sitrus Berry
Storm Drain | Relaxed
252 HP / 196 Def / 60 SpD
- Giga Drain
- Ancient Power
- Protect
- Earth Power/Gastro Acid
Cradily here synergizes wonderfully with Tyranitar, as the two only share a Fighting weakness. 252 HP / 196 Def and Relaxed to survive Terrakion's Close Combat, with the rest in SpD for more overall bulk. I aimed for survivability with this spread, but alternatively you could swap the SpD EVs for SpA to pick up a few more KOs. He absorbs Water attacks with Storm Drain. Ancient Power over Rock Slide due to it being more powerful in Doubles, plus that nifty chance to boost every stat. Giga Drain hurts Water, Rock, and Ground-types. Protect is essential. The final slot is either Earth Power to hit Steel-types or Gastro Acid for some gimmicky, yet effective, plays if done right. You can elimnate Parental Bond, TerraBeat strategies, and Pixilate, leaving Sylveon spamming Normal-type Hyper Voices.
Landorus
Landorus@ Choice Band
Intimidate | Adamant
172 HP / 244 Atk / 92 Spe
- Earthquake
- Rock Slide
- Superpower
- U-Turn
I found it suiting to bestow the Choice item upon Landorus. However, since you're not running max Speed there's no point in the Scarf, so I gave him the Choice Band instead. Yache Berry's good for surprises, but the surprise is gone in best-of-three. In this case, Choice Band is a good option. I made a tiny tweak to your EV spread, adding 1 point of speed and still surviving Sucker Punch. U-Turn was added to hit Cresselia & co. for super-effective damage, and spreading Intimidate is always nice.
Salamence
Mega Mence is a dominating force in VGC, that's for sure. However, he and Landorus make really poor comrades. Besides, between their Earthquakes you could potentially wipe out most of your team.
You said that Sand was a very anti-meta weather. You know what's even more anti-meta? Dual weather, that's what.
Charizard@ Charizardite Y
Drought | Timid
252 SpA / 252 Spe / 4 HP
- Heat Wave
- Solar Beam
- Protect
- Overheat
Mega Charizard not only eliminates your Ice weakness but serves as a possibly better Rain check than Tyranitar due to Sun nerfing their Water attacks and having Solar Beam coverage. I chose a simple EV spread to maximize damage output and Timid for as much speed as possible. Heat Wave is a handy Sun-boosted STAB spread move. Solar Beam slams Water- and Rock-types. Protect because this is VGC. Overheat is in case you need a nuke.
Klefki
Klefki isn't as useful now thanks to the new teammates. It doesn't really do anything that another member couldn't do; in fact now, there is another Steel type that can help.
Aegislash@ Weakness Policy/Colburr Berry
Stance Change | Quiet
252 HP / 252 SpA / 4 SpD
- Shadow Ball
- Flash Cannon
- Wide Guard
- King's Shield
Aegislash is generic, but useful. He stops Rock Slide for Charizard with Wide Guard, absorbs Fighting attacks for Tyranitar and Cradily, plus checks Metagross and his Psychic friends with Shadow Ball. I would suggest customizing the EVs a little, but it's not necessary. Flash Cannon hits Ice-types for Landorus and Rock-types for Charizard, plus Fairies in general. King's Shield is what Protect dreams it would be; use it on a well-placed Knock Off and you get the Weakness Policy boost and screw the attacker with a -2 Attack. Alternatively, you could run Culburr Berry to avoid being KOd by Dark attacks.
Milotic
Milotic@ Rocky Helmet
Competitive | Modest
252 HP / 36 Def / 164 SpA / 4 SpD / 52 Spe
- Hydro Pump
- Ice Beam
- Icy Wind
- Protect
As your yourself stated, offensive Milotic needs the Competitive boost in order to do any damage. With Klefki gone, Milotic will enjoy having something to do when there is no boosts to be had, so I gave her speed control in Icy Wind. Protect replaces Recover because in this fast-paced meta there is little time for recovery. It has its uses, but I believe you'll find Protect keeps you alive longer. Do some testing with both. One of your Water STABs had to be removed to fit Icy Wind, and Hydro Pump is better suited for offensive Milotic. You could also trade Ice Beam for Icy Wind and keep Scald. Since the Sitrus Berry is being used on Cradily, Rocky Helmet was the next option.
Leads
Tyranitar + Cradily + Aegislash
This will be your preferred lead against Rain and Perish Trap teams. Mega T-Tar is usually bulky enough to pull off a Dragon Dance, and the odds improve with Storm Drain. But if you see a potential Fighting attack, head for the hills. Aegislash can help Zard fight of Sand teams with Wide Guard.
Landorus + Charizard
Basically free Earthquake spam. Sun nullifies Water attacks, Charizard's Fire attacks take care of Ice, and Lando can check Rock- and Electric- types. This lead tends to suffer from Rotom-W, so bring Cradily in the back.
Milotic + Cradily
A fun little gimmick that's won me a few matches. Have Milotic spam water attacks for Cradily to soak up until he can destroy almost everything with boosted STABs. I did this with Azumarill and Gastrodon, and it's taken me back from some 3-2s.
There's my rate. I'm sorry if I made too many changes, but I do hope that I made the team better. (I added a separate part in the 'Comments'.) If you're uncomfortable with these changes they can be debated, and I'm sure an agreement will be made. I wish you the best of luck in your tournament. May the RNG be with you.
