From Bulbapedia, the community-driven Pokémon encyclopedia.
Each item has a number used to identify it in any game. The following list enumerates them according to the way they are stored in any Generation II Game Boy Color game.
Items exclusive to Pokémon Crystal are Teru-sama in Pokémon Gold and Silver. When viewed in Pokémon Stadium 2, they show up as the exclusive item from Pokémon Crystal, even if the games connected to the Transfer Pak are Pokémon Gold and Silver.
HM08 to HM10 are used here, in that order
Index number 000, if held by a Pokémon, causes the game to behave as if the Pokémon is not holding an item. In the international releases of Pokémon Crystal, it crashes the game due to an oversight.
Teru-sama with index numbers 006 and 056 actually have an effect after being modified to include the USE option onto them, which reveals that they are actually leftover items from the Generation I games. 006 works as a faulty version of the old Town Map while 056 is the Poké Flute and works exactly the same; however, it does not affect the sleeping Snorlax in Vermilion City and the audio only plays if used on a sleeping Pokémon outside of battle.
Teru-sama with index number 190, if forced to have the USE option, triggers an invalid pointer, indicating that it was likely never intended to support the function.
Index numbers 194 and 195 both contain an item named "TM04". The first index (194) is the real TM04. The second index (195) is a unused and useless item that shares the same name, is stored in the Items pocket of the Bag, and has no USE option. The same applies to index numbers 219 and 220, in which both are "TM28". When held by a Pokémon, the name of both unused TM04 and TM28 is instead displayed as Berry (Japanese: きのみ Berry). Otherwise, these two "fake" TMs behave like Teru-sama.
Index numbers 250 to 254 have the name of HMs but they are stored in the Items pocket of the Bag and behave like Teru-sama otherwise. In addition, index numbers 250 to 252 are internally used by Pokémon Crystal while displaying the list of moves taught by the Move Tutor.
All these items can be sold for 19660.
Index number 255 is similar to its Generation I counterpart in that it does the same thing as the Cancel option and hides items below it. However, it does not trigger the USE/GIVE/TOSS/SEL/CANCEL menu, it cannot be held by a Pokémon, and it cannot be purchased or sold.