SM Ubers New, I think this is good team. Feedback?

[Ellie T]

Hey I am new to this... stuff... and I think this is a pretty good team. I am quite aware, however, that when one thinks something that thought is usually (always) wrong (topology in a nut-shell btw). Therefore I want ta see how bad I am actually at building teams. This team capped at like 1700 but idk what that means.

Latias-M

Latias @ Latiasite
Ability: Levitate
Shiny: Yes
EVs: 252 HP / 76 Def / 4 SpD / 176 Spe
Timid Nature
IVs: 0 Atk
- Defog
- Toxic
- Recover > Roost
- Grass Knot

There is this pokemon named P-don that exists. I wanted a hard counter and I have seen few people use Latias-M even though it is rated on the viability thread (awesome resource btw), so I decided to build a team around it. Hard-switching into things such as all P-don lacking dragon pulse and most P-ogre sets is this Latias's job. I really like how a lot of people use P-don as a stealth rock setter so I can just switch in and get rid of those pesky things. I was running a healing wish set originally but found my team benefited a lot more if Latias could switch into things it could check throughout the match (plus aparently recover is better than roost, but I like roost's animation better). Grass knot is ran over draco meteor because I found that the spa drops hindered me a lot in matches, plus I can now worry less about some P-ogre sets who were taking at least one pokemon earlier on.

P-don

Groudon @ Red Orb
Ability: Drought
EVs: 248 SpA / 100 SpD / 160 Spe
Mild Nature
- Rock Polish
- Precipice Blades
- Fire Blast
- Hidden Power [Ice]

This is mixed rock-polish p-don and I hope most people reading this already know the ins and outs of the mon better than me because it seems to be a common threat in the meta-game. Like I implied earlier, the original idea was healing wish latias with two powerful set up sweepers. I was running double dance, but I found I really like this set pairing with double dancing dusky dusk mane (say that 5 times fast xd). Most matches I try to keep this thing healthy if there is an xern; that way I can keep two xern checks alive. The raw power of fire blast allows me to weaken up checks dusk-mane shares with P-don (like lugia and some arceus forms). The ability to circumvent other shared checks (like zygod) is another very notable trait of the set that I like.

Dusk-Mane

Necrozma-Dusk-Mane @ Solganium Z
Ability: Prism Armor
EVs: 248 Atk / 8 SpD / 252 Spe
Adamant Nature
- Rock Polish
- Swords Dance
- Sunsteel Strike
- Earthquake

I see every-other dusk mane run automatize but I really do not like that animation. Anyhow, this is my second win-con that also functions as my primary xern check. A lot of people fear this set, (or those like it but I am obviously not running ultra if I have Latias-M) so I am usually using this pokemon to wall-break. Boy, can it wall-break! Sunraze Searing Smash (what is with all this alliteration) is an amazing nuke that, when not played dumb, can at the very least soften up pokemon that may give p-don trouble. Overall I look at the synergy of my set up sweepers and like them a lot

Xern

Xerneas @ Choice Scarf
Ability: Fairy Aura
EVs: 4 Def / 252 SpA / 252 Spe
Modest Nature
IVs: 0 Atk
- Moonblast
- Focus Blast/ hp fire
- Aromatherapy
- Thunder

There are certain pokemon such as marshadow and yvetal that just feed on dusk mane offensively. Therefore I am using xern to combat that offensive power back at them. Looking at my team you can see that 3 of my pokemon really fear marshadow and the other two are not really checks. I also had worries about dd zygod among other things. Xern patches up these weaknesses and more. Aromatherapy helps me combat stall teams, and thunder lets me maybe get a cheap hit of ho-oh or hurt P-ogre. Honestly I have not clicked focus miss once and idk if hp fire is better or not. I worry about this thing dying prematurely while Marshadow is still large and have thought about revamping the team with Arceus Fairy, but I cannot get it to work.

Marshadow

Marshadow @ Life Orb
Ability: Technician
EVs: 252 Atk / 4 Def / 252 Spe
Jolly Nature
- Spectral Thief
- Close Combat
- Shadow Sneak
- Rock Tomb

After playing quite a few games I saw how awesome this pokemon is (orginally I had like a noob mon Blazekin in this slot). The stab combo, along with that speed, and priority; really allows me the threaten teams after one of my pokemon faint (is this what they call revenge killing xd). I find that Latias-M and Xern invite Dusk Mane onto the field. As long as Marshadow is alive, I cannot be swept so easily! Rock tomb is there because the speed drop really plays with some setup sweepers and I fear ho-oh.
Originally, I was going to run sash but I noticed I wanted more power and I added this next pokemon.

T-tar

Tyranitar @ Shuca Berry
Ability: Sand Stream
EVs: 252 HP / 252 Def / 4 SpD
Impish Nature
- Foul Play
- Rock Tomb
- Toxic
- Stealth Rock

At this point I found that I really needed a secondary check to things such as Yvetal, a good primary switch in to Ho-oh, stealth rock, and maybe a neat little lure for Necrozema. I also wanted all of this without sacrificing too much on offensive presence because there are a lot of set up sweepers I would prefer to let marshadow deal with. This Ttar set is what I came up with. Foul-Play really plays (ay) on ubers plethora of high attacking mon (95 bp stab is not too shabby). Rock tomb may seem sub-optimal but it allows me to keep some pokemons in a speed range while sacking T-tar and still hits Ho-oh hard enough. Most games I am just sacking this pokemon at the right time and maybe I get rocks up in the process or a good toxic. Most necrozema's are not aware that this pokemon soft checks them until it is too late.

Importable

Latias @ Latiasite
Ability: Levitate
Shiny: Yes
EVs: 252 HP / 76 Def / 4 SpD / 176 Spe
Timid Nature
IVs: 0 Atk
- Defog
- Toxic
- Roost
- Grass Knot

Groudon @ Red Orb
Ability: Drought
EVs: 248 SpA / 100 SpD / 160 Spe
Mild Nature
- Rock Polish
- Precipice Blades
- Fire Blast
- Hidden Power [Ice]

Necrozma-Dusk-Mane @ Solganium Z
Ability: Prism Armor
EVs: 248 Atk / 8 SpD / 252 Spe
Adamant Nature
- Rock Polish
- Swords Dance
- Sunsteel Strike
- Earthquake

Xerneas @ Choice Scarf
Ability: Fairy Aura
EVs: 4 Def / 252 SpA / 252 Spe
Modest Nature
IVs: 0 Atk
- Moonblast
- Focus Blast
- Aromatherapy
- Thunder

Marshadow @ Life Orb
Ability: Technician
EVs: 252 Atk / 4 Def / 252 Spe
Jolly Nature
- Spectral Thief
- Close Combat
- Shadow Sneak
- Rock Tomb

Tyranitar (M) @ Shuca Berry
Ability: Sand Stream
EVs: 252 HP / 252 Def / 4 SpD
Impish Nature
- Foul Play
- Rock Tomb
- Toxic
- Stealth Rock

Overall I really think this is a strong team. I tried to keep two checks to strong meta-game defining pokemons (except for P-don who Latias-M handles very well). Ultra-necrozema sets with sunsteel strike worry me a bit. Losing xern early while marshadow is still around and having to rely on a 50-50 sneak really worries me. I am very new to this so I would love to see other ideas on this team and things I am overlooking. Oh, and excuse my grammar; I am American.