Mechanics & Damage-Calc Reference

The technical source of truth behind every “2HKO” and “OHKO” in this guide. ADV runs on Gen-3 (RSE) cartridge math, and that math differs from every later generation in ways that decide games: the physical/special split is by type, crits deal ×2, the only Choice item is the Choice Band, and the type chart has no Fairy and Steel resisting both Ghost and Dark. If you are coming from a modern gen, this is the page that re-wires your instincts. Everything here is implemented verbatim in the interactive damage calculator — use this chapter to understand the numbers it gives you, and to do the math in your head mid-game when you can’t open a calc.

This is a reference chapter. It does not present sets — for sets and matchups see the top threats and common cores. Here we lock down why the breaks in building aggressive offense actually break.

The damage formula

Gen 3 computes damage with a single integer chain. Truncate (floor) after the core integer math and after every modifier multiplication — rounding error is real and changes break ranges, so a mental calc has to floor at each step the same way the cartridge does.

Step 1 — the core

base = floor( floor( floor( (2*Level/5 + 2) * Power * A ) / D ) / 50 ) + 2

Computed strictly left-to-right with truncation:

1. levelTerm = floor(2 * Level / 5) + 2 — at Level 100 this is 42.
2. × Power (the move’s base power).
3. × A — the attacker’s relevant offensive stat (Attack for physical-type moves, Sp.Atk for special-type moves), already including item and stat-stage modifiers (see below).
4. floor( ÷ D ) — divide by the defender’s relevant defensive stat (Defense or Sp.Def), then floor.
5. floor( ÷ 50 ).
6. + 2.

The critical implementation detail: items like Choice Band, Thick Club, and Light Ball fold into the stat A before the core — they are not a post-core “Other” multiplier. So a Choice Band Tyranitar’s Attack is multiplied by 1.5 and then fed into the formula. Likewise, Explosion and Self-Destruct halve the target’s Defense D inside the core (D/2), which is why Boom is so much stronger here than in later gens — it effectively doubles the hit. CB Metagross Explosion has a high chance to OHKO Skarmory precisely because of this halving (see Metagross).

Step 2 — the modifier chain

Each modifier is applied in this fixed order, flooring after each multiplication:

Two clamps to remember: the random factor uses /100, not the old /255 form — there are exactly 16 damage rolls, and the calc enumerates all of them. And if the type multipliers reduce damage to 0 without it being a true immunity, the value is clamped to a minimum of 1 before the random roll.

Critical hits

A crit in Gen 3 is ×2 damage, not ×1.5 (that ×1.5 is a Gen-6+ change — do not use it here). Base crit rate is 1/16 (6.25%).

What a crit ignores, and what it does not:

• Ignores the attacker’s negative offensive stat stages (an Intimidate’d attacker crits at full Attack).
• Ignores the defender’s positive defensive stat stages (a Calm Mind’d Suicune’s +Sp.Def is bypassed; a Curse Snorlax’s +Def is bypassed).
• Ignores Reflect and Light Screen.
• Does NOT ignore burn. A burned physical attacker still does half damage on a crit (this is a Gen-3 quirk vs Gen 1). Weather, items, STAB, and type all still apply on a crit too.

Practically, the engine uses max(unmodified, boosted) for the attacker’s offense and min(unmodified, lowered) for the defender’s defense on a crit — it never hurts you to crit.

The crit rate is a summed stage, not a single flag:

High-crit-ratio moves include Slash, Crabhammer, Razor Leaf, Karate Chop, Aeroblast, Cross Chop, and Sky Attack. No ability raises crit rate in Gen 3 — Super Luck and Sniper are Gen-4+. The offensive takeaway: crits punch through the defensive boosts (Curse Snorlax, CM Suicune) that your wallbreakers otherwise grind against, so a 6.25% “free” break is always lurking on the setup walls you’re trying to overload.

The physical/special split is by TYPE

This is the single most important Gen-3 mechanic and the one most likely to trip up a modern player. The damage category is a property of the move’s type, not the individual move.

The consequences are everywhere and they shape every set in this guide:

• Crunch, Pursuit, and Knock Off are Dark-type → SPECIAL. Tyranitar’s Crunch runs off Sp.Atk, not Attack — which is why mixed Tyranitar is a thing, and why a Choice Band (Attack-only) Tar leans on Rock Slide / Earthquake / Focus Punch, not Crunch.
• Shadow Ball is Ghost-type → PHYSICAL. Gengar’s Shadow Ball runs off its mediocre Attack, so offensive Gengar attacks specially with Thunderbolt / Ice Punch and reserves the physical slot for Explosion (also physical). See Gengar.
• Rock Slide, Earthquake, Body Slam, Meteor Mash are physical; Fire Blast, Surf, Ice Beam, Thunderbolt are special. Standard.
• Hidden Power splits by its derived type: HP Flying / Ground / Bug / Rock are physical, while HP Fire / Grass / Ice are special. So a Choice Band attacker wants HP Flying/Bug, while Magneton’s HP Fire and MixMence’s HP Grass run off Sp.Atk.

The rule for building: a Choice Band set (which only boosts Attack) should carry only physical-TYPE damage moves. A special-typed move on a Band set fires off uninvested Sp.Atk and gets nothing from the item — the classic build error.

The one exception: Beat Up. It is Dark-typed (so “special” by the table), but each of its hits is computed from a party member’s base Attack, so Choice Band neither helps nor hurts it. CB Dugtrio’s Beat Up is the intended, legal Blissey-chip tool — not a miscategorization. See Dugtrio.

Item multipliers

Gen 3’s item economy is austere, and that austerity defines the speed-control problem. All stat multipliers fold into the stat before the core.

What does NOT exist in Gen 3, and you must never write onto a set:

• No Choice Scarf — the reason there is no item-based speed. Speed comes from base stats, Dragon Dance / Agility, Salac Berry, or paralysis. This is the central tension of every offense in this guide.
• No Choice Specs — special attackers run Leftovers; there is no special analogue to the Band.
• No Life Orb, no Focus Sash, no Toxic Orb / Flame Orb. Use Leftovers, Lum Berry, Chesto Berry, or the pinch berries (Salac / Liechi / Petaya / Starf).

Soul Dew (×1.5 Sp.Atk and Sp.Def in Gen 3) exists in the data but is banned in ADV OU — and its holders Latias/Latios are Uber regardless. Do not build with it.

Hidden Power

Both the type and the base power of Hidden Power derive from the six IVs, read in stat order HP, Atk, Def, Spe, SpA, SpD. The trap: Speed comes before the special stats — getting the order wrong is the most common HP-calc mistake.

Type — let a..f be the least significant bit (IV % 2) of each stat in that order:

typeIndex = floor( (a + 2b + 4c + 8d + 16e + 32f) * 15 / 63 )

typeIndex 0–15 maps to: Fighting, Flying, Poison, Ground, Rock, Bug, Ghost, Steel, Fire, Water, Grass, Electric, Psychic, Ice, Dragon, Dark. Hidden Power is never Normal and never the (nonexistent) Fairy.

Base power — let u..z be bit 1 ((IV >> 1) & 1) of each stat in that order:

basePower = floor( (u + 2v + 4w + 8x + 16y + 32z) * 40 / 63 ) + 30

Base power ranges 30–70 in Gen 3 (it was only fixed at 60 from Gen 6 — another modern habit to drop). Most competitive spreads sacrifice a couple of points to hit a desired type at near-max BP (e.g. 70-BP HP Flying for Aerodactyl/Salamence, ~70-BP HP Fire for Magneton). The derived type then runs through the physical/special map above to decide whether the move uses Attack or Sp.Atk.

Weather

Weather modifiers slot into position 4 of the chain. Sand is the default because Tyranitar is everywhere.

The aggressive read: Sand is a clock that wears down your own frail sweepers and the bulky Waters you’re trying to break — so either embrace it (Tyranitar / Aerodactyl ignore the chip; Flyers like Zapdos and Salamence take it but pressure through it) or carry your own weather setter to override it. Remember Explosion/Self-Destruct halve the target’s Defense in the core, not as a weather-style chain multiplier.

Stat & HP formulas

EVs cap at 510 total, 252 per stat. (The old “255” notation is legacy — stats round per 4 EVs, so 252 is effectively the max useful investment.) IVs run 0–31.

HP    = floor( (2*Base + IV + floor(EV/4)) * Level / 100 ) + Level + 10
Stat  = floor( ( floor( (2*Base + IV + floor(EV/4)) * Level / 100 ) + 5 ) * Nature )

• Nature is one of {1.1, 1.0, 0.9}, applied after the +5 and then floored. Nature never affects HP.
• Shedinja always has 1 HP (not OU-relevant, but the canonical exception).
• At Level 100 the inner term simplifies to 2*Base + IV + floor(EV/4), which makes the common benchmarks (e.g. the 101-HP Substitute on offensive Suicune) easy to verify by hand.

The Gen-3 type chart — read this, don’t trust modern instinct

Every effectiveness in this guide is computed by multiplying the two defender multipliers from the Gen-3 chart. The chart differs from Gen 6+ in ways that matter constantly:

• There is NO Fairy type in Gen 3. No Fairy attacker, no Fairy defender, anywhere.
• Steel RESISTS both Ghost and Dark (×0.5 each). This is the single most common ADV error. Tyranitar’s Crunch (Dark) and Gengar’s Shadow Ball (Ghost) are resisted by every Steel — Skarmory, Metagross, Forretress, Jirachi, Magneton. (Steel only became neutral to Ghost/Dark in Gen 6.) If a source tells you “Ghost/Dark → Steel = 2×,” it is wrong for Gen 3.
• Ghost → Normal = 0 (immune), and Normal/Fighting → Ghost = 0 the other way. Ghost → Psychic = 2 and Dark → Psychic = 2 (this is the Crunch/Shadow Ball value that matters — vs Psychics, not vs Steels).
• Ground → Flying = 0. Earthquake whiffs on the Flyers and Levitators, which is why Dugtrio can’t trap them.

A few worked dual-type examples used throughout the guide (multiply the two columns):

That last pair is the trap. Tyranitar’s own Crunch is resisted by Skarmory, and Gengar’s Shadow Ball is resisted by Tyranitar — neither is the “super-effective Ghost/Dark spam” a modern player expects. The full 17×17 chart is what the calculator implements; when in doubt, multiply the two columns (type multipliers stack cleanly to 0 / 0.25 / 0.5 / 1 / 2 / 4).

The interactive calculator

All of the above is implemented on the damage calculator page: the by-type split, the ×2 crit, Choice Band ×1.5 folded into the stat, Explosion’s Defense-halving, the Gen-3 type chart (no Fairy, Steel resisting Ghost/Dark), Hidden Power derivation, weather, and the R ∈ [85,100] 16-roll spread. Use it to confirm the OHKO/2HKO ranges quoted in top threats and sample teams against your exact EV spreads — the difference between a guaranteed break and a 50% roll is usually a few EVs.

Sources

The mechanics and formulas on this page were synthesized from the following references:

• ADV OU Viability Ranking & Metagame Discussion (canonical maintained tier list, McMeghan OP)
• ADV OU Teambuilding/Strategy: Archetypes and Cores — A Data-Driven Approach
• ADV OU Sample Teams and Team Dumps
• Dragon Dance Tyranitar Offense by McMeghan (RMT)
• ADV OU HO DragMag (RMT)
• Smogon RS (Gen 3) Strategy Pokedex — pokemon set/EV root
• Smogon RS OU format dex
• Smogon RS Uber format dex (Gen 3 Uber banlist)
• Magnet Pull vs Steel-type allies in Gen 3 (confirms Magnet Pull traps Steel in Gen 3)
• Bulbapedia — Damage category (physical/special split is by type until Gen IV)
• Bulbapedia — Critical hit (1/16 base, ×2, ignores stages/screens not burn)
• Bulbapedia — Hidden Power/Calculation (type & BP from IVs)
• Bulbapedia — Damage (Gen 3 formula & modifier chain)
• Bulbapedia — Sandstorm (no Rock SpD buff until Gen IV)
• Smogon DP Damage Formula (structurally identical chain reference)
• Pokémon Showdown Gen 3 damage calc (random factor /100, R in [85,100])
• smogon/damage-calc generation-specific mechanics
• Generation 3 Ubers Viability Ranking Thread (confirms Gen 3 Uber tier incl. Latios/Latias/Wobbuffet)
• Smog Issue 10 — A Step Back: The Advance Metagame
• Smogon/pokemon-showdown Gen 3 formats-data.ts & rulesets.ts (tier tags + clause definitions)