Rock Smash

Author(s): MrHam88.
Research: pokeheartgold.

This page is a guide to Rock Smash encounters and item drop in Pokémon HeartGold and SoulSilver. It covers how the game determines wild encounters, how item drops are calculated, the structure of the map-specific data archive, and the locations of the hardcoded item tables in the ROM's overlay.

info

In HGSS, Rock Smash interactions trigger a two-step check:

1. Wild Pokémon Encounter: Checked first using the map's overworld encounter tables, defined in NARC /a/0/3/7.
2. Item Drop: Rolled only if the wild encounter check fails. The drop rate and item table selection are map-dependent, defined in NARC /a/2/5/3.
3. Item Tables: The contents of each item table are defined in Overlay 1.

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Glossary

• NARC /a/2/5/3 (NARC Index 255): The map metadata archive for Rock Smash containing drop rates and table configurations.
• Encounter Rate: The base probability of triggering a wild encounter when smashing a rock.
• Drop Odds: The base probability (out of 100) of revealing an item when smashing a rock.
• Table Type: An identifier that maps a location to one of three hardcoded lists of item rewards.

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Wild Pokémon Encounters

Before rolling for items, the game checks if a wild encounter occurs. This is handled by a generic encounter calculation.

How the game checks for encounters

The game reads the encounterRate_rockSmash byte at offset 0x02 of the loaded encounter data table, and editable via DSPRE's Encounter Editor.

• If this rate is 0, a wild encounter is impossible, and the game proceeds immediately to the item drop check.
• If it is non-zero, the encounter rate can be modified by the leading party Pokémon's ability:
  • 2.0x multiplier: Arena Trap, No Guard, or Illuminate.
  • 0.5x multiplier: Stench, Quick Feet, White Smoke, or Snow Cloak (only if weather is currently Hail).
• The final adjusted rate is capped at 100%.
• The game rolls LCRandom() % 100. If the roll is less than the final encounter rate, a battle begins against one of the two species defined in the map's rockSmashSlots (species and min/max levels defined from offset 0x78 in the encounter table, and editable via DSPRE's Encounter Editor.).

If a wild battle is triggered, no item drop check is performed.

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Item Drop Rates

If the wild encounter roll fails, the game rolls for an item drop using data from NARC /a/2/5/3.

NARC Structure and Identity

• File path: data/a/2/5/3
• Indexing: Each member file in this NARC corresponds directly to a Map Header ID (i.e. member N = Map Header N).
• File Layout: Every member file is exactly 4 bytes long, mapping to the following struct:

Offset	Field	Size	Description
0x00	odds	uint16 (little-endian)	Base item drop chance (0 to 100). 0 disables item drops for this map.
0x02	type	uint16 (little-endian)	Drop table selector (0 = Default, 1 = Ruins of Alph, 2 = Cliff Cave).

Base Odds Modifiers

If the base odds are non-zero, they can be modified by:

• +5% if the lead party Pokémon has the ability Suction Cups, Magnet Pull, or Keen Eye.
• +5% if the player is followed by a Pokémon that executed the Rock Smash HM. The final drop rate is capped at 100%. If LCRandom() % 100 < final_drop_rate, an item is awarded.

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Item Selection Logic and Tables

Once an item drop is confirmed, the game rolls a random slot index (0 to 7) based on the following probability distribution:

Slot	Base Probability
0	25%
1	20%
2	10%
3	10%
4	10%
5	10%
6	10%
7	5%

Ability Shift (Serene Grace / Super Luck)

If the leading party Pokémon has the ability Serene Grace or Super Luck, and the rolled index is less than 7, the index is incremented by 1 (shifting the index to rarer slots, e.g. slot 0 is skipped and slot 7 becomes a 15% chance).

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Hardcoded Item Tables in ROM (Hex Editing)

The three drop tables are hardcoded as static array constants within Overlay 1 (field). In the ROM binary, this corresponds to ov001.bin.

Because the game compiles with version-specific #ifdef blocks, the Ruins of Alph and Cliff Cave tables contain different species depending on whether you are editing HeartGold or SoulSilver.

Table Offsets in ov001.bin

In HeartGold (decompressed ov001.bin), these three tables are compiled sequentially starting at offset 0x23D04 (RAM address 0x02209604):

Vanilla Item Drop Tables

Below is the layout of the 8 slots in the three hardcoded item tables, showing the values for both version compile types (HeartGold and SoulSilver):

Slot	Probability	Default Table (type == 0) Offset: 0x23D14	Ruins of Alph Table (type == 1) Offset: 0x23D04	Cliff Cave Table (type == 2) Offset: 0x23D24
0	25%	Max Ether	HG: Red Shard SS: Blue Shard	Max Ether
1	20%	Revive	HG: Yellow Shard SS: Green Shard	Pearl
2	10%	Heart Scale	HG: Helix Fossil SS: Dome Fossil	Big Pearl
3	10%	Red Shard	Max Ether	HG: Red Shard SS: Blue Shard
4	10%	Blue Shard	HG: Blue Shard SS: Red Shard	HG: Yellow Shard SS: Green Shard
5	10%	Green Shard	HG: Green Shard SS: Yellow Shard	HG: Claw Fossil SS: Root Fossil
6	10%	Yellow Shard	Old Amber	HG: Claw Fossil SS: Root Fossil
7	5%	Star Piece	Max Revive	Rare Bone