TM04 (useless)

The useless TM04 in the items pack.

The useless TM04 (hex:C3) is a glitch item in Pokémon Gold, Silver and Crystal. It belongs to the items pocket and is a useless copy of the actual TM04. It sells at a Poké Mart for 19660 Pokédollars.

The description of this item is "Attacks 5 turns with rising power."; the same as the actual TM04 (Rollout).

Purpose

The Pokémon Crystal disassembly project offers this explanation for the duplicate TM04 and TM28, pertaining to the conversions of Pokémon Red, Blue, and Yellow catch rates into Pokémon Gold, Silver and Crystal held items and early development of Generation II.

There was originally a good reason for these two gaps!

Pokémon traded from RBY to GSC have their catch rate interpreted as their new held item. This was planned early on in development, so some items were given indexes corresponding to appropriate Gen 1 catch rates:

$03 = 3: BRIGHTPOWDER is for Articuno, Zapdos, Moltres, and Mewtwo
$1E = 30: LUCKY_PUNCH is for Chansey
$23 = 35: METAL_POWDER is for Ditto
$3C = 60: SILVER_LEAF is for 10 Pokémon
$4B = 75: GOLD_LEAF is for 13 Pokémon
$96 = 150: MYSTERYBERRY is for Clefairy
$AA = 170: POLKADOT_BOW is for Jigglypuff
$B4 = 180: BRICK_PIECE is for Machop
Yellow was also being developed then, and it did the reverse, altering some Pokémon's data after they're caught to correspond to appropriate Gen 2 items:

Starter Pikachu's catch rate byte is overwritten with 163 = $A3 for LIGHT_BALL
Wild-caught Kadabra's catch rate byte is overwritten with 96 = $60 for TWISTEDSPOON
(Yellow also directly changed Dragonair's catch rate to 27 and Dragonite's to 9, but this seems to have been only for adjusting their difficulty, since those meaninglessly correspond to PROTEIN and ANTIDOTE.)

Most catch rates were left as gaps in the item list, and transformed into held items via the TimeCapsule_CatchRateItems table in data/items/catch_rate_items.asm. For example, the 52 Pokémon with catch rate 45 would hold the gap ITEM_2D, except that gets transformed into BITTER_BERRY.

But a few Pokémon end up with weird items. Abra has a catch rate of 200, or $C8; and Krabby, Horsea, Goldeen, and Staryu have a catch rate of 225, or $E1. Those indexes correspond to the items TM_PSYCH_UP and TM_ICE_PUNCH, which seem like random choices—because they are.

The TMs and HMs span from indexes $BF to $F9. However, as we can see in pokegold-spaceworld, they originally spanned $C4 to $FF. For some reason they were shifted down by 5 during development.

Before the index shift, the gap ITEM_C3 would have been at index $C8, and ITEM_DC at $E1. In other words, they would have neatly corresponded to the catch rates for those five Pokémon! Then they would have held BERRY when traded through the Time Capsule (since the gap items get transformed via TimeCapsule_CatchRateItems).