Polished Crystal Breeding Guide: IVs, Natures, Egg Moves & Abilities

Introduction

Breeding produces eggs at Day Care. You control IV inheritance, natures, abilities, and egg moves. It is also the route to competitive Pokémon, Masuda Method shiny hunting, and moves outside normal learnsets.

Quick answer: how to breed a battle-ready Pokémon

Choose the offspring species, then set its nature with an Everstone, improve inherited IVs with a Destiny Knot and good parents, add egg moves with Mirror Herb or chain breeding, and use the appropriate ability item when you need a Hidden Ability. For the shortest workflow, jump to Optimized Breeding Workflow. For shiny breeding odds, see the Shiny Hunting guide.

Breeding workflow at a glance

1. Choose the species and confirm its compatible parent or egg group.
2. Decide the target nature, IVs, ability, form, Poké Ball, and egg moves.
3. Prepare the relevant parent and held items, then leave the pair at a Day Care location.
4. Collect and hatch eggs, checking the result against the traits you are targeting.
5. For shiny hunting, use the shiny odds guide for the rate comparison instead of duplicating its mechanics here.

How to breed a specific Pokémon

For any target species, use this decision path before leaving the parent Pokémon at Day Care. Pokémon in the No Eggs/Undiscovered group cannot breed; genderless species require Ditto, while other species can use Ditto or a compatible parent from a shared egg group.

1. Confirm the offspring species. The female parent determines the species, or the non-Ditto parent does when breeding with Ditto. Check the target’s egg groups and use the compatibility checker if you are unsure which parent can breed with it.
2. Set the traits you actually need. Choose the nature, IV targets, ability or form, Poké Ball, and egg moves before selecting held items. This avoids replacing a parent later and losing an inheritance rule you still needed.
3. Prepare the parents. Use an Everstone for the target nature, a Destiny Knot for broader IV inheritance, and Mirror Herb or a breeding chain for egg moves. Hidden Ability and form inheritance have separate rules; they are not guaranteed by the nature item.
4. Breed, hatch, and replace selectively. Leave the pair at the Day Care, hatch eggs on Route 34, and keep offspring only when they improve the trait you are targeting. For shiny hunting, follow the separate shiny odds guide rather than mixing probability advice into the inheritance checklist.

This gives you a route for “how do I breed X?” without pretending that every species uses the same parent, egg-move, ability, or form setup.

Breeding checklist

Before collecting eggs, confirm these decisions in order:

This checklist is a planning aid, not a replacement for the species-specific rules in the sections below.

Who This Guide Is For

This guide is for players who want to:

• Build competitive or battle ready Pokémon
• Breed Hidden Abilities and egg moves efficiently
• Optimize IVs, natures, and shiny odds without wasted time

If you’re just dropping Pokémon off at Day Care and hoping for the best, you’ll miss most of what Polished Crystal’s breeding system offers.

---

What's New in Polished Crystal

Polished Crystal changes:

• Mirror Herb – Transfer egg moves between parents at Day Care^[1]
• Ability Capsule/Patch – A held item raises the Hidden Ability branch to 25% with one parent, or 50% when both parents hold one^[2]
• Mr. PKMN's traded Ditto – Trade a Red Scale for a documented 6IV shiny Ditto with a different OTID^[3]
• Nidorina/Nidoqueen breedable – Now in Monster/Field groups (vanilla had them in Undiscovered)^[4]
• Form inheritance – 50/50 when same-species parents have different forms^[5]
• Poké Ball inheritance – Offspring will inherit the mother/non-Ditto's ball. If both parents share the same species, offspring can inherit a ball from either parent^[5]

Breeding Compatibility Tool

Instead of memorizing egg groups, use the interactive compatibility checker below. It shows every Pokémon that can breed with your selected species, grouped by shared egg group - ideal for planning egg moves and breeding chains.

---

Egg Groups

Egg groups determine breeding compatibility. Two Pokémon breed if they share at least one group (except Undiscovered). Offspring species comes from the female parent (or non-Ditto parent when breeding with Ditto).^[6]

Most players won’t need to memorize egg groups. Instead, focus on Pokémon that belong to multiple groups, since they act as bridges for egg move transfer. Marill is a common early-game example that can connect Fairy and Water 1 breeding chains.

Polished Crystal uses 15 egg groups:

• Amorphous – Gastly, Grimer, Wobbuffet
• Bug – Caterpie, Weedle, Scyther
• Dragon – Dratini, Larvitar, Kingdra
• Fairy – Clefairy, Togepi, Snubbull
• Field – Pikachu, Eevee, Growlithe
• Flying – Pidgey, Spearow, Hoothoot
• Grass – Oddish, Chikorita, Sunflora
• Human-Like – Machop, Hitmonlee, Mr. Mime
• Mineral – Geodude, Onix, Shuckle
• Monster – Bulbasaur, Charmander, Nidoran-M
• Water 1 – Squirtle, Totodile, Marill
• Water 3 – Tentacool, Shellder, Corsola
• Water 2 – Goldeen, Magikarp, Qwilfish
• Ditto – Ditto only, breeds with most groups
• Undiscovered – Cannot breed (babies and legendaries): Pichu, Togepi, Lugia

Pokémon in multiple groups act as breeding bridges. Marill (Water 1 + Fairy) can transfer egg moves between those groups.

---

Gender Ratios

Gender ratios affect breeding efficiency since offspring species comes from the female parent (or non-Ditto parent).

• 100% Female / 0% Male – Chansey, Miltank
• 75% Female / 25% Male – Clefairy, Vulpix
• 50% Female / 50% Male – Pikachu, most Pokémon
• 25% Female / 75% Male – Growlithe, Abra
• 12.5% Female / 87.5% Male – Starters: Chikorita, Cyndaquil, Totodile, Bulbasaur, Charmander, Squirtle, Eevee
• 0% Female / 100% Male – Tauros (must use Ditto)
• Genderless – Magnemite, Staryu, Porygon (must use Ditto)

---

Egg Move Inheritance

Egg moves are moves only accessible through breeding. Male parent moves transfer first, then female moves. The move must be in the offspring's egg move pool.^[7]

Key rules to know:

• Male parent moves take priority
• Move must exist in offspring's egg move pool
• Offspring hatch with inherited moves already learned
• Multiple egg moves transfer when both parents have moves in the pool

Mirror Herb

Mirror Herb transfers egg moves between Pokémon at Day Care:^[1]

• Ensure there are empty move slots on the Pokémon you want to inherit a move. You can delete moves using the Move Deleter in Blackthorn City
• Give this Pokémon the Mirror Herb to hold. You can purchase a Mirror Herb in Goldenrod Harbor
• Get any other Pokémon that knows the egg move you want to inherit, irrespective of egg group or gender, and place both in the Day Care together
• Each step has 1/256 chance to copy an egg move to the Mirror Herb holder

Chain breeding is sometimes still needed. If Pokémon A knows a move but can't breed with Pokémon B, breed A with C (which shares groups with both), then breed C with B. Mirror Herb usually eliminates this.

---

Hatch Cycles and Steps

Eggs hatch after a certain number of cycles. Each cycle is ~256 steps.^[8]

• 5 cycles (1,280 steps) – Magikarp
• 10 cycles (2,560 steps) - Pichu
• 15 cycles (3,840 steps) - Caterpie
• 20 cycles (5,120 steps) – Starters, most Pokémon
• 25 cycles (6,400 steps) - Elekid, Smoochum, Magby
• 30 cycles (7,680 steps) - Fossils, excluding Aerodactyl
• 35 cycles (8,960 steps) - Aerodactyl, Eevee
• 40 cycles (10,240 steps) – Dratini, Larvitar, Happiny, Munchlax

Faster hatching:

• Flame Body or Magma Armor in party: 2× multiplier on number of cycles completed per 256 steps^[9]
• Oval Charm: 2× multiplier^[10]
• Both stack: the hatch-cycle decrement is multiplied by 4, although actual elapsed time also depends on movement and egg production^[9]

---

Ditto Breeding

Ditto is especially valuable for breeding with the following categories of Pokémon:^[11]

• Male-only: Tauros
• Genderless: Magnemite, Staryu, Porygon
• Skewed gender ratios (easier than finding females)

Non-Ditto parent determines offspring species.

Find Ditto on Route 35 or Cerulean Cave postgame.^[12] Mr. PKMN's traded Ditto can be useful when its documented IVs and different OTID match your breeding goal (see below).

Mr. PKMN's traded shiny Ditto

Mr. PKMN trades Red Scale for 6IV Shiny Ditto:

• Documented 31 IVs in all stats
• Different OTID activates the breeding shiny bonus
• Get Red Scale from catching or defeating Red Gyarados at Lake of Rage

---

Day Care Locations

Day Care is in Goldenrod City's south side. Route 34 below it is good for hatching.

Compatibility messages:

• "They seem to get along very well!" – Same species, different OTs (fastest eggs)
• "They seem to get along." – Same species same OT, or different species different OT
• "They don't seem to like each other." – Different species, same OT (slow eggs)
• "They prefer to play with other Pokémon." – Incompatible (no eggs)

---

When to Start Breeding

Early game breeding is mostly useful for:

• Egg moves you can’t get otherwise
• Trying to get a Hidden Ability
• Nature control via Everstone

Full competitive breeding is best saved until:

• You have access to Mr. PKMN's documented 6IV shiny Ditto
• You can get Destiny Knot and Everstone
• You catch Flame Body Pokémon (Okay this is optional, but it speeds up hatching a lot)

---

Competitive Breeding

Battle-ready Pokémon need specific IVs, natures, and abilities.

Competitive Breeding at a Glance

1. Choose Hidden Ability → Ability Patch/Capsule
2. Choose IVs → Destiny Knot + 6IV Ditto
3. Add egg moves → Mirror Herb or chain breeding
4. Choose nature → Everstone
5. Hatch efficiently → Flame Body + Oval Charm

IV Inheritance

IVs (Individual Values) range 0–31 per stat. Higher = better stats at level 100.

Extra Math: Polished build IVs just range from 0-15, with the IV being equivalent to a modern game IV after doing a x2+1 calculation, e.g. a Polished IV of 14 = 29 in modern (14x2=28+1=29)

How IVs pass down:^[13]

• Default: Three random IVs from parents
• Destiny Knot: Five IVs from parents (one still random)
• Power items (Power Weight, Power Bracer, etc.): Guarantees specific stat IV from holder

Method:

1. Get parents with good IVs (or use Mr. PKMN's traded Ditto if it fits your goal)
2. Give one Destiny Knot
3. Breed until offspring has better IVs
4. Replace parent with better offspring
5. Repeat

Nature Inheritance

Natures give +10% to one stat, -10% to another.

Common competitive natures:

• Adamant (+Attack, -Sp. Atk): Physical attackers
• Jolly (+Speed, -Sp. Atk): Fast physical attackers
• Modest (+Sp. Atk, -Attack): Special attackers
• Timid (+Speed, -Attack): Fast special attackers
• Bold (+Defense, -Attack): Physical walls
• Calm (+Sp. Def, -Attack): Special walls

Passing nature: Everstone on parent = 100% nature inheritance.^[14]

Catch wild Pokémon with Synchronize (Abra from Goldenrod Game Corner) to get specific natures easier.

Ability Inheritance

Ability Capsule/ Ability Patch held by one parent raises the Hidden Ability branch to 25%; if both parents hold one, it rises to 50%. These are probabilities, not guarantees.^[2][15]

Female (or non-Ditto) parent:

• 60% chance to pass its current ability, with other outcomes handled by the breeding routine^[15] For ways to obtain Hidden Abilities before breeding, see the Wonder Trade guide and the relevant wild-encounter data rather than assuming a universal rate.

Form Inheritance

Same-species parents with different forms: 50/50 chance for each form.

Different species: Female (or non-Ditto) parent's form.^[5]

Everstone only affects nature, not form.

Pokéball Inheritance

Same species: Either parent's ball (50/50).

Different species: Female (or non-Ditto) parent's ball.^[5]

Shiny Breeding - Masuda Method

Masuda method increases shiny odds through different OTIDs (Original Trainer IDs).^[16]

In Polished Crystal:

• Needs different OTIDs, not different languages
• Mr. PKMN's Shiny Ditto has different OTID = auto-activates method^[3]
• Much higher shiny chance than normal breeding/wild encounters^[16]
• Stacks with Shiny Charm^[17]
• Parent shininess doesn't affect offspring IVs^[16]

Optimized Breeding Workflow

1. Get Mr. PKMN's documented 6IV shiny Ditto if its IVs and different OTID fit your goal (trade a Red Scale from Red Gyarados)
2. Set the ability you want on the parent. If you need a Hidden Ability, have one or both parents hold an Ability Capsule/Ability Patch to raise the branch to 25% or 50%; neither outcome is guaranteed.
3. Catch Synchronize Pokémon for each nature you need (Abra at Goldenrod Game Corner)
4. Give target nature parent Everstone
5. Get egg moves via breeding or Mirror Herb
6. Give the other parent Destiny Knot, breed with the Ditto, and swap in offspring with better inherited IVs and the desired ability as you go.
7. Hatch with Flame Body/Magma Armor plus Oval Charm to multiply hatch-cycle decrement by 4.

Nidoran Breeding Mechanics

Nidoran-F eggs hatch as either sex (50/50).^[18]

Nidorina and Nidoqueen can breed (Monster/Field groups). This differs from main games where they can't breed.^[4]

---

Common Breeding Mistakes

• Breeding with Ditto when you need egg moves (Ditto cannot pass moves)
• Forgetting Everstone when hunting for specific natures
• Using Ability Capsules incorrectly and expecting guaranteed Hidden Abilities
• Ignoring Flame Body/Magma Armor, doubling hatch time unnecessarily
• Chain breeding when Mirror Herb would be faster

---

Sources and Implementation Notes

All mechanics in this guide are verified directly against Polished Crystal’s engine logic and scripting. Source links reference the exact routines or data tables used in-game.

[1] Mirror Herb egg move transfer

• Mirror Herb item effect — engine/events/happiness_egg.asm

[2] Ability Capsule/Patch and Hidden Ability breeding

• Ability Patch implementation — engine/items/item_effects.asm
• Ability Capsule implementation — engine/items/item_effects.asm
• Hidden Ability breeding inheritance — engine/events/daycare.asm

[3] Mr. PKMN's 6IV Shiny Ditto trade

• Mr. PKMN event scripting — maps/MrPokemonsHouse.asm

[4] Nidorina/Nidoqueen breeding and egg groups

• Species data for Nidoran line — data/pokemon/base_stats/nidoran_f.asm
• Species data for Nidorina — data/pokemon/base_stats/nidorina.asm
• Species data for Nidoqueen — data/pokemon/base_stats/nidoqueen.asm

[5] Form and Poké Ball inheritance

• Form inheritance logic — engine/events/daycare.asm
• Poké Ball inheritance logic — engine/events/daycare.asm

[6] Egg group compatibility and species parent rules

• Breeding compatibility checks — engine/pokemon/breeding.asm
• Egg group definitions in species data — data/pokemon/base_stats

[7] Egg move inheritance rules

• Egg move selection and priority — engine/pokemon/breeding.asm

[8] Hatch cycles and step count

• Base hatch cycles per species — data/pokemon/base_stats
• Egg-hatching step handling — engine/pokemon/breeding.asm

[9] Flame Body and Magma Armor hatching modifier

• Flame Body ability effect — engine/battle/abilities.asm
• Magma Armor ability effect — engine/battle/abilities.asm
• Egg-hatching speed checks — engine/pokemon/breeding.asm

[10] Oval Charm and egg production rate

• Oval Charm item effect — engine/pokemon/breeding.asm
• Day Care egg generation — engine/pokemon/breeding.asm

[11] Ditto breeding compatibility rules

• Ditto special-casing in breeding — engine/pokemon/breeding.asm

[12] Ditto encounter locations

• Route 34 & 35 encounter data — data/wild/johto_grass.asm
• Cerulean Cave encounter data — data/wild/kanto_grass.asm

[13] IV inheritance, Destiny Knot, and Power items

• IV inheritance without items — engine/pokemon/daycare.asm
• Destiny Knot IV selection — engine/events/daycare.asm
• Power item IV override — engine/events/daycare.asm

[14] Everstone nature inheritance

• Everstone nature check — engine/events/daycare.asm

[15] Ability inheritance chances

• Breeding ability inheritance — engine/events/daycare.asm
• Ability-related data constants — constants/pokemon_data_constants.asm

[16] Masuda method and shiny odds

• Masuda method shiny calculation — engine/events/daycare.asm

[17] Shiny Charm interaction with breeding

• Shiny Charm item effect — engine/events/daycare.asm
• Shiny rate calculation with Charm — engine/events/daycare.asm

[18] Nidoran-F eggs hatching as either gender - [Nidoran egg gender logic

---