Need help with this team. SM OU.

Question

Hello everyone, I need help with my current team right now. I am thinking of a few changes on my team. Any opinions would be gladly appreciated. :)

Team:

Therian (Landorus-Therian) @ Assault Vest  
Ability: Intimidate  
EVs: 252 Atk / 4 SpD / 252 Spe  
Jolly Nature  
- Earthquake  
- Stone Edge  
- U-turn  
- Knock Off  
*This thing is really good right now, being able to check some of the threats that eat my team, If someone has a better EV spread, I would love to get it. I was thinking of going scarf instead, but that extra spdef is so good to pass on.

Wish (Jirachi) @ Choice Scarf  
Ability: Serene Grace  
EVs: 252 Atk / 4 SpD / 252 Spe  
Jolly Nature  
- Iron Head  
- Heart Stamp  
- U-turn  
- Healing Wish  
*This is my revenge killer #1 and Tapu killer as well. With all the Tapus running amok (looking at you lele), I thought I needed a steel type that's fast. I was thinking of replacing Healing wish with either Fire punch to get Bulu.

Wackamole (Marowak-Alola) (M) @ Thick Club  
Ability: Lightning Rod  
Shiny: Yes  
EVs: 248 HP / 16 Atk / 112 SpD / 132 Spe  
Adamant Nature  
- Shadow Bone  
- Bonemerang  
- Fire Punch  
- Stealth Rock 
*When I quit back then during the 3rd gen (Emerald), I thought there's no poke that will make me want to pick up another game again, but there it was. His design is so cool and I love his current moveset right now, being able to setup rocks when an opportunity arrives. 

Matador (Tapu Bulu) @ Choice Band  
Ability: Grassy Surge  
EVs: 248 HP / 252 Atk / 8 SpD  
Adamant Nature  
- Wood Hammer  
- Horn Leech  
- Megahorn  
- Superpower  
*Grassy Terrain Boosted Wood Hammer, nuff said. I just need a better EV spread for this fella.

Umi (Toxapex) (F) @ Black Sludge  
Ability: Regenerator  
EVs: 252 HP / 252 Def / 4 SpD  
Bold Nature  
IVs: 0 Atk  
- Toxic  
- Haze  
- Scald  
- Recover  
*My off-stall to go mon. Wow this thing really shines against setup sweepers, and when paired with bulu, this thing never dies LOL. 

Tapu Lele @ Life Orb 
Ability: Psychic Surge  
EVs: 4 HP / 252 SpA / 252 Spe  
Modest Nature  
IVs: 0 Atk  
- Psychic  
- Moonblast  
- Hidden Power [Fire]  
- Taunt  
*Lastly, I needed a M-Venusaur check, as well as another anti lead to scare away those enemy stallers. I'm very torn though, since I have no defoggers to keep Marowak-A on my team.

Problems:
1. First of all, I really, really need a defogger or a spinner. I am in between of using Fini or Latios but do not know which one to replace.
2. Jirachi and Gross, which is better? With all the fairies flying around, I really need a good steel type
3. Any suggestions on the current builds would be appreciated. So far this team is really weak to Serperior (once its boosted, it eats through my team) I thought of adding a fast Revenge killer like Dragonite or Talonflame but dunno which one to take off my Team.

Hopefully this will also help some other people looking into making their very own OU S/M Team.

Comments

If you are going to use defensive Lando, Assault Vest is pretty inferior to a PhysDef set with Rocks. Then, you could put a fourth move onto Marowak instead. I'm curious as to what that Marowak spread accomplishes. Toxapex is a bit out of place on this mostly offensive team, and is passive enought that it would sap momentum, so I'd suggest replacing it with a defogger. Latios could be a good choice, as offensive Heatran does a number on your team. Twisted Spoon should be considered on Lele to bluff a choice item, though it is entirely preference. As for your Jirachi or Metagrossquestion, I think Jirachi is a fine choice for this team. U-Turn grabs some opportunities for the rest of your team to launch some hard hits off.

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Thanks for your feedback! lol Yes iv been having problems with toxapex on my team, I took your suggestion and placed Latios instead and its doing wonders on the SR problem. Although I think the reason why I put toxapex on my team was my fear of being setup fodder when I try and switch out. Anyway, I'm going to try the phydef lando you suggested. That spread for marowak was something that I just found, which the speed evs help it outspeed chansey, aegislash. Then dumped everything else on spdef to take some special hits.  On lele, should I stay modest if I do add twistedspoon? or could I go timid? Lastly, yes that confirms my thoughts on jirachi, that hes maybe much better than gross for this team. I appreciate your input. :)

Edit: So I've tried the new lineup and it seems like I'm falling short on checking some setup sweepers. Bulu's spread seems to make him really slow to keep up to checking some of the threats if someone has a better spread I would really appreciate it.