Mechanics that Define National Dex OU

What separates gen9nationaldex from Gen 9 OU and from older NatDex. Assumes you know how the base mechanics work — this is about what’s on, what’s off, and why it shapes the meta. Megas + Z-Moves are legal.

Ruleset at a glance

gen9nationaldex runs Standard NatDex OU. Practically:

Banlist headline (beyond the Uber/AG mon list): abilities — Arena Trap, Moody, Power Construct, Shadow Tag; items — King’s Rock (fully banned), Quick Claw, Razor Fang; moves — Assist, Baton Pass, Last Respects, Shed Tail. (Shed Tail and Baton Pass banned = no substitute or stat hand-offs to prop up offense; you earn your setup honestly.)

1. Typing is permanent — build around fixed matchups

Defensive and offensive typing is locked for the entire game; there is no on-demand type-change to brick a hit, break a wall, or add surprise coverage. Every downstream conclusion in this guide traces to that.

The teambuilding takeaway: walls are trustworthy, so the meta rewards resilient Bulky Offense / Balance, and offense has to win by sequencing, not by a one-button matchup flip (hazards + dual breakers sharing no checks + speed control). This is exactly why the offense the reader wants to build is demanding — and why it’s worth a dedicated build guide.

Why typing is permanent here, and what that changes if you’re coming from Gen 9 OU: Appendix: The Tera Ban.

2. Mega Evolution — the single-slot economy

One Mega per team. Megas evolve the turn you select a move (the Mega’s stats — including Speed — apply that turn). Because the slot is exclusive, the format’s strong Megas are in direct competition:

• Diancie-Mega — Magic Bounce hazard deterrent + mixed breaker.
• Scizor-Mega — Technician Bullet Punch priority + SD pivot (the premier priority on offense).
• Charizard-Mega-Y — Drought special nuke (sun’s payoff).
• Charizard-Mega-X — Tough Claws DD physical sun breaker.
• Latios-Mega — fast special breaker/pivot.
• niche: Venusaur-Mega (Thick Fat BO anchor), Tyranitar-Mega (sand/Pursuit), Sableye-Mega (Magic Bounce stall), Mawile-Mega (TR breaker), Medicham-Mega (wallbreaker), Gyarados/Gardevoir/Houndoom-Mega.

Stats undercount Megas — usage is partly logged under the base species, so the listed % for Diancie/Scizor/Char-Y/Latios understates how often they’re actually run. Pick your Mega first when building; everything else fits around it.

3. Z-Moves — your one per-game trump

One Z-crystal, one use. Two flavors matter:

• Damage Z — a one-time burst that lets a breaker punch a hole it otherwise can’t. Z-output BP scales: base BP 90-99→175, 100-109→180, 110-119→185, 120-129→190, 130-139→195, and 140+→200.
• Status Z — boosting side effects (e.g. Z-Conversion, Z-Splash) and full-heal-on-status-move plays.

Common lines you’ll meet: Gholdengo + Steelium-Z (Make It Rain → Corkscrew Crash), Kyurem + Groundium-Z, Volcarona + Firium-Z, Tapu Lele / Dragonite / Ceruledge Z-breakers, and Tapu users + Tapunium-Z (Guardian of Alola) when they run Nature’s Madness.

Corkscrew Crash caveat: it is the Z-output of Steelium-Z + Make It Rain, never a move you “run.” Any set listing Corkscrew Crash as a chosen move is wrong. (And remember: one Z and one Mega per team, max.)

4. Future Sight — the engine that powers pivot-offense

Future Sight fires a delayed special Psychic hit two turns after use into the target slot. It can hit a different Pokémon than the one originally targeted, but the current slot occupant’s typing and grounded/terrain state still matter at resolution — Dark-types are immune, Steels/Psychics resist it, and Psychic Terrain only boosts it into grounded targets while the terrain is active. Paired with a slow pivot (Teleport / Chilly Reception / U-turn), it lets you double up: the FS lands as your breaker comes in, so the opponent eats the FS and the breaker’s hit on the same wall in the same turn. Slowking-Galar (Future Sight + Chilly Reception + Regenerator) and Slowbro are the premier emitters; this is the backbone of the “delayed-damage offense” pattern in common cores.

5. The abilities that warp building

• Good as Gold (Gholdengo) — immune to targeted status-category moves aimed at it: no Defog on it, no Toxic, no Will-O, no Encore, no Taunt, no Spore. This is why Gholdengo denies hazard removal so hard. Exceptions: damaging moves still work — Nuzzle bypasses Good as Gold (it’s a damaging move that paralyzes) — and all-field moves like Haze can still reset boosts.
• Magic Bounce (Diancie-Mega, Hatterene, Sableye-Mega) — reflects status-category hazards and status moves back. It is a strong countermeasure to conventional lead hazard-setting, but damaging hazard moves such as Ceaseless Edge and Stone Axe bypass the bounce; offense often needs that kind of workaround or just to overwhelm it.
• Regenerator (Alomomola, Toxapex, Slowking-Galar, Tornadus-T, Amoonguss, Slowbro) — heal 1/3 on switch. This is the glue tax offense must pay: these pivots reset their HP every time they leave, so you can’t chip them out passively — you have to break them.
• Booster Energy (Paradox mons: Iron Valiant, Iron Treads, Raging Bolt, Iron Moth, Iron Hands, Iron Crown) — on switch-in, boosts the highest stat ×1.3 (×1.5 for Speed) once. Defines the “Booster line” benchmarks: a Booster-Speed Iron Valiant outruns the relevant unboosted field short of Regieleki-style outliers; a Booster-Attack/SpA one trades speed for a breaking boost. Know which each opponent is running — it changes the speed math (see speed tiers).
• Multiscale (Dragonite) — halves damage at full HP; you must chip it (hazards!) before you can revenge it, which is why Dragonite loves hazard-free fields and Heavy-Duty Boots.
• Supreme Overlord (Kingambit) — +10% damage per fainted ally; the late-game cleaner scales with the carnage offense creates, making it a natural offense win-condition.

6. The hazard / removal war

Because typing is fixed and Regenerator walls reset, hazard chip is offense’s primary currency. The contest:

• Setters: Stealth Rock (Landorus-T, Garchomp, Ting-Lu, Heatran, Great Tusk, Iron Treads), Spikes (Ferrothorn, Gliscor, Ting-Lu, Garchomp, Samurott-H’s Ceaseless Edge), Toxic Spikes (Toxapex, Iron Moth), Sticky Web (Glimmora niche).
• Removal: Rapid Spin (Great Tusk, Iron Treads), Defog (Zapdos, Corviknight, Tornadus-T), Court Change (Cinderace).
• Denial: Gholdengo blocks Rapid Spin (Ghost typing) and blocks Defog (Good as Gold) — the single most important reason hazard-stack offense functions. Magic Bounce mons stop conventional status-move setters, while damaging hazard moves still work. Ghost-types block your spin too.

For an offense builder: decide early whether you’re a hazard-stack team (lead setter + Gholdengo to deny removal) or a boots/removal team (Great Tusk / Iron Treads to keep your own side clean for frail breakers). Trying to do both half-way is how offense ends up doing neither.

7. Weather & terrain (still live)

• Sun — Drought (Charizard-Mega-Y, Torkoal, Ninetales) → fire nukes + Chlorophyll sweepers (Venusaur). A real offense subtype; see archetypes.
• Sand — Sand Stream (Tyranitar-Mega, Hippowdon) → chip + SpD-rock boost; enables Pursuit-trap / Grassy-Glide structures.
• Rain — Drizzle (Pelipper) → Swift Swim sweepers (Swampert-Mega, Barraskewda), Archaludon Electro Shot, Manaphy.
• Terrain — Electric (Tapu Koko), Psychic (Tapu Lele — blocks priority targeting grounded Pokémon, fuels Psychic STAB), Grassy (Rillaboom — Grassy Glide priority, halves EQ), Misty (Tapu Fini). Terrain and weather coexist; only another terrain replaces terrain, and only another weather replaces weather. Stack them only when their roles support the same game plan.

8. Quick legality checklist (apply to every set you build)

• Imported sets cleared against the Appendix legality checklist.
• ≤ 1 Mega and ≤ 1 Z-Move on the team.
• No banned ability/item/move (esp. King’s Rock, Baton Pass, Shed Tail).
• No Uber/AG mon (Roaring Moon, Dragapult, Flutter Mane, Kyurem-Black, Magearna, Zamazenta-Crowned, Mega Blaziken, etc.). Usage data is already legal-only — if it’s in the tiers, it’s legal.