National dex is honestly the most fun format just because of the insane possibilities. Every single pokemon and every single gimmick put together into one. That's why almost all my teams are national dex. This one is an offensive style team with little setup. Its all about using the stats and types of my pokemon to take out the opponents team. High defense, high attack pokemon on one end that can beat anything on that end, physical or special. The first three act as the core members, with the last 3 being a sort of shell that gives the team more stability
Nihilego @ Assault Vest
Ability: Beast Boost
Tera Type: Rock
EVs: 240 SpA / 16 SpD / 252 Spe
Timid Nature
IVs: 0 Atk
- Hidden Power [Grass]
- Power Gem
- Sludge Wave
- Clear Smog
A really strong pokemon, nihilegos really high 131 spe.def and strong 127 spe.atk make it able to fight off special attackers. Its rock type also is weak to water, grass, fighting, and ice. Two physical types, one it can beat over with its poison typing and one without a strong spe.attacker. When it comes to special attackers, the only things that really threaten it without setup are keldeo, and Serperior. It ohkos serperior and tanks a +2 leaf storm w/o assault vest or any sp.def evs. It can threaten other rock, water and ground types with Hp Grass, clear smog wipes out any sweeper pokemon and beast boost allows to get better kill power after its already beaten something, making it sweeper potential. However, it cant break walls such as heatran and ferrothorn, being 4× weak to steel. Its easily threatened by iron Crown, Mmawile, and Mscizor, especially with how weak it is physically.
Cinderace @ Heavy-Duty Boots
Ability: Libero
Tera Type: Grass
EVs: 252 HP / 164 SpD / 92 Spe
Careful Nature
- Court Change
- Pyro Ball
- Will-O-Wisp
- U-turn
A classic pivot build. U turn out of threats, court change for Hazard control, wisp to cripple physical attackers, and pyro ball for damage. Nothing to really say about it. Its simply a solid build
Ferrothorn @ Rocky Helmet
Ability: Iron Barbs
Tera Type: Water
EVs: 252 HP / 160 Def / 96 SpD
Relaxed Nature
IVs: 0 Spe
- Leech Seed
- Curse
- Toxic
- Gyro Ball
A stall build, with emphasis on beating physical attackers. If threatened by a Gouging Fire, Ceruledge, Or MXCharizard, tera water makes sure you wont be beaten easily. Defensively, the only real way to beat it efficiently is using a 4× strong fire type or switching to a special attacker. Otherwise this'll chip down and cripple anything it faces. However, it struggles against other tanks like Heatran. Ferrothorn struggles against slower pokemon because of gyro ball, and especially against strong defenders and attackers like Mscizor, Mbanette and Zamazenta.
Thundurus-Therian @ Choice Scarf
Ability: Volt Absorb
Tera Type: Flying
EVs: 252 SpA / 4 SpD / 252 Spe
Modest Nature
IVs: 0 Atk
- Focus Blast
- Volt Switch
- Wildbolt Storm
- Tera Blast
Choice scarf ThundurusT is powerful. It threatens toxapex and targets corviknight and gargancls weaker sp.def. Volt switch is for any need to pivot and get out in a instant bad mu. Focus miss threatens Heatran and ferrothorn with a 2hko, with no way to hitting thundurus back for strong damage. Overall a solid shell pokemon
Corviknight @ Leftovers
Ability: Pressure
Shiny: Yes
Tera Type: Ground
EVs: 252 HP / 64 Atk / 192 Def
Impish Nature
- Roost
- Defog
- U-turn
- Brave Bird
Corviknight is a wall, and has been that way since its been in the game. However, it also comes with decent attack as well. This build is the classic defensive pivot with its last evs in attack instead of sp.def for that offensive boost. Both pivots do the same job, get rid of hazards and be a nuisance, then go out and wait. Defog can easily be replaced with iron defense, however once cinderace dies nobody will be able to do his job and hazards can kill this team. So i opted for this instead.
Tapu Lele @ Psychic Seed
Ability: Psychic Surge
Tera Type: Psychic
EVs: 184 SpA / 72 SpD / 252 Spe
Modest Nature
IVs: 0 Atk
- Moonblast
- Psyshock
- Psychic
- Calm Mind
A slot holder, but a solid. This is one of my favourite builds to use, with psychic seeds and calm mind allowing it to take on any special attacker. It can do this better than most with the combo of psyshock and psychic terrain boosting its power. It 2hkos almost everything and isnt threatened by a lot, even dark types cant reliably 1v1 this month. Moonblast ohkos Darkrai, the biggest threat to it, and it tanks all of its moves unless its boosted by nasty plot and runs coverage. However, this team struggles in a lot of situations, mostly in breaking walls. If there's any good suggestions, let me know
Nihilego @ Assault Vest
Ability: Beast Boost
Tera Type: Rock
EVs: 240 SpA / 16 SpD / 252 Spe
Timid Nature
IVs: 0 Atk
- Hidden Power [Grass]
- Power Gem
- Sludge Wave
- Clear Smog
A really strong pokemon, nihilegos really high 131 spe.def and strong 127 spe.atk make it able to fight off special attackers. Its rock type also is weak to water, grass, fighting, and ice. Two physical types, one it can beat over with its poison typing and one without a strong spe.attacker. When it comes to special attackers, the only things that really threaten it without setup are keldeo, and Serperior. It ohkos serperior and tanks a +2 leaf storm w/o assault vest or any sp.def evs. It can threaten other rock, water and ground types with Hp Grass, clear smog wipes out any sweeper pokemon and beast boost allows to get better kill power after its already beaten something, making it sweeper potential. However, it cant break walls such as heatran and ferrothorn, being 4× weak to steel. Its easily threatened by iron Crown, Mmawile, and Mscizor, especially with how weak it is physically.
Cinderace @ Heavy-Duty Boots
Ability: Libero
Tera Type: Grass
EVs: 252 HP / 164 SpD / 92 Spe
Careful Nature
- Court Change
- Pyro Ball
- Will-O-Wisp
- U-turn
A classic pivot build. U turn out of threats, court change for Hazard control, wisp to cripple physical attackers, and pyro ball for damage. Nothing to really say about it. Its simply a solid build
Ferrothorn @ Rocky Helmet
Ability: Iron Barbs
Tera Type: Water
EVs: 252 HP / 160 Def / 96 SpD
Relaxed Nature
IVs: 0 Spe
- Leech Seed
- Curse
- Toxic
- Gyro Ball
A stall build, with emphasis on beating physical attackers. If threatened by a Gouging Fire, Ceruledge, Or MXCharizard, tera water makes sure you wont be beaten easily. Defensively, the only real way to beat it efficiently is using a 4× strong fire type or switching to a special attacker. Otherwise this'll chip down and cripple anything it faces. However, it struggles against other tanks like Heatran. Ferrothorn struggles against slower pokemon because of gyro ball, and especially against strong defenders and attackers like Mscizor, Mbanette and Zamazenta.
Thundurus-Therian @ Choice Scarf
Ability: Volt Absorb
Tera Type: Flying
EVs: 252 SpA / 4 SpD / 252 Spe
Modest Nature
IVs: 0 Atk
- Focus Blast
- Volt Switch
- Wildbolt Storm
- Tera Blast
Choice scarf ThundurusT is powerful. It threatens toxapex and targets corviknight and gargancls weaker sp.def. Volt switch is for any need to pivot and get out in a instant bad mu. Focus miss threatens Heatran and ferrothorn with a 2hko, with no way to hitting thundurus back for strong damage. Overall a solid shell pokemon
Corviknight @ Leftovers
Ability: Pressure
Shiny: Yes
Tera Type: Ground
EVs: 252 HP / 64 Atk / 192 Def
Impish Nature
- Roost
- Defog
- U-turn
- Brave Bird
Corviknight is a wall, and has been that way since its been in the game. However, it also comes with decent attack as well. This build is the classic defensive pivot with its last evs in attack instead of sp.def for that offensive boost. Both pivots do the same job, get rid of hazards and be a nuisance, then go out and wait. Defog can easily be replaced with iron defense, however once cinderace dies nobody will be able to do his job and hazards can kill this team. So i opted for this instead.
Tapu Lele @ Psychic Seed
Ability: Psychic Surge
Tera Type: Psychic
EVs: 184 SpA / 72 SpD / 252 Spe
Modest Nature
IVs: 0 Atk
- Moonblast
- Psyshock
- Psychic
- Calm Mind
A slot holder, but a solid. This is one of my favourite builds to use, with psychic seeds and calm mind allowing it to take on any special attacker. It can do this better than most with the combo of psyshock and psychic terrain boosting its power. It 2hkos almost everything and isnt threatened by a lot, even dark types cant reliably 1v1 this month. Moonblast ohkos Darkrai, the biggest threat to it, and it tanks all of its moves unless its boosted by nasty plot and runs coverage. However, this team struggles in a lot of situations, mostly in breaking walls. If there's any good suggestions, let me know
As an offensive attacker with Power Herb and STAB Meteor Beam, its not that bad (although significantly better in NDUU), but as a specially defensive wall, it struggles. Poison/Rock is pretty bad typing, being weak to Ground, Water and Psychic while not having very good resistances or immunities either. I'd rather use Toxapex or Mega Venusaur as a specially defensive Poison-type than Nihilego since they can also heal reliably. 
The set itself isn't bad, but the EVs are kinda strange, and these odd spreads are repeated throughout the team. Do they do anything in particular or are they just randomly put? I'm on mobile rn but there is a Cinderace analysis for NDOU so you'd rather use that spread than this one. 
Again like Cinderace the EV spread isn't the same as the standard spread. Ferrothorn is also a poor setup sweeper and would rather use its bulk to offer utility to its team in Spikes or Stealth Rock or Thunder Wave. Leftovers could also be used over Rocky Helmet to have some form of recovery alongside Leech Seed.
In NDUU this set could probably be solid but in NDOU it struggles. You'd rather use Tapu Koko who's stronger because of Electric Terrain while still being fast enough to outspeed most things and not being weak to Stealth Rock. Being tera-reliant to use its secondary STAB is also not good since Ferrothorn and Nihilego would want tera as well, while being locked into a Flying-type move allows Iron Boulder or Garganacl to setup on you for free.
Not a bad mon, I'm not to sure about the EV spread but I'd rather use Tera Dragon to deal with Rain/Sun teams better, especially since Thundurus should be switching into Electric-type moves anyways. 
If you're running Calm Mind there's no real need for Psychic Seed, especially since it puts forward a "one-time only" mindset which setup Lele doesn't need to have. Fightinium Z Focus Blast or Psychinium Z are better choices for a strong nuke option which this team kinda lacks.