Items are things that have certain effects in battle. Some items only work if they are held by a Pokémon. You can only attach one item to a Pokémon in the Second, Third and Fourth generations, so that means RBY Pokémon will not use Items in player vs. player battles. There are several items are that very good to attach, there are items that you shouldn't even bother with, and there are some items that people think are good but in reality they are not. This section will list some recommended items to attach and some items to avoid. Of course, this mostly applies only for competitive battling, and some items that are extremely bad can become useful in-game because it is easy to get and NPCs do not think very much by themselves.
Generally, items that boost one stat (like X Attack or Guard Spec. in GSC) or items that boosts one type (such as Twistedspoon or Charcoal) are bad. This is because they do not benefit the Pokémon entirely, but just a stat or one or two attacks. The old saying is, "When in doubt, use Leftovers." The reason why is below.
 Recovery Items
This item is great. Every turn, it heals one-sixteenth (1/16) of your maximum HP. This does not sound very good, but think about it. If you last 8 moves, then your HP has healed by half of your maximum HP! If you end up in the yellow or red zone after 8 turns, then you know that Leftovers has saved you. This is the most used item on every competitive team, since between 4 and 5 out of 6 Pokémon will hold Leftovers. To recap, you heal automatically without using a healing move.
 Shell Bell
This is another healing item, but it acts quite differently. When you attack someone, Shell Bell will restore one-eighth (1/8) of the damage taken by your opponent back to you. While this sounds wonderful, it's not. First, it can only recover HP if you use a move that damages your opponent. Second, for Shell Bell to roughly equal the power of Leftovers, that move must take away half of your opponent's HP. Since that is a hard quota to get to, Leftovers is superior. However, Shell Bell is a good substitute for Leftovers on Pokémon that you use to attack often and if you are too lazy (or have no way to trade) to get 4 to 5 leftovers by trading.
 Miracleberry or Lum Berry
These items heal every Status Effect and Confusion immediately on the user. However, it can only be used once per battle. This item is mostly found on attackers, who cannot be hindered by Paralysis killing its Speed or Burn killing its Attack. Miracleberry is for GSC and Lum Berry is for RSE/FRLG/DP.
 Mint Berry or Chesto Berry
These items only heal the Sleep Status Effect, but they are sometimes preferred over Miracleberries and Lum Berries. Pokémon with the move "Rest" usually have this berry attached, since it is a free 100% HP Recovery move and you wake up right away. If you have Miracleberry or Lum Berry attached, an opponent might Paralyze you and you will cure the Paralysis, making Miracleberry or Lum Berry not usable for Rest again. Remember that Rest also recovers Status Effects such as Paralysis.
 Stat Changing and Related Items
 Scope Lens
This item increases the chance of getting a Critical Hit. If used properly on certain Pokémon, each time you attack you could have a 50% chance of dealing a Critical Hit.
 Quick Claw
This item gives you a 10% chance of going first. True that a 10% chance is bad and true that this item is generally not useful, but in some very rare cases, it could be useful.
This item gives you a 20% chance of evading your opponent's attack. Basically, this item gives a 0.8x multiplier to every attack coming at you. If your opponent attacks you with Fire Blast (accuracy: 80%), then Fire Blast's accuracy is now 80% x 0.8 = 64%. It's rather unreliable, but like Quick Claw, there are some rare applications to it, especially when attached to a Pokémon with high defenses using Double Team.
 Pokémon-Specific Items
 Light Ball
This item gives Pikachu an x2 bonus to special attack. Pikachu can become incredibly powerful with this item, especially if it also has Surf.
 Thick Club
This item doubles the attack of Cubone and Marowak. It's only for Marowak, but unlike X Attack, which gives s 10% boost to Attack, this gives a 100% boost to Attack, so it's worth using.
 Soul Dew
This item gives both Special Attack and Special Defense a 1.5x multiplier when attached to Latias or Latios. Like Thick Club, it is Pokémon-specific, and it makes Latias and Latios extremely powerful. Beware that some battlers will forbid this item on Latias and Latios.
 Metal Powder
This item gives both Attack and Defense a 1.5x multiplier when attached to Ditto. Like Thick Club, it is Pokémon-specific.
 Third-Fourth Generation Items
 Choice Band (RSE/FRLG, D/P only)
This item multiplies your Attack status (not Special Attack also) by 1.5x. While doing so, you can only use one move from your moveset, unless you switch out. This might sound unappealing or pure unusable to some people, but when used correctly, it works wonders.
 White Herb (RSE/FRLG, D/P only)
This item rids Status Changes inflicted upon you either by your opponent, by the user, or by a user's team-mate (or party-mate if you so want to call it that). However, this item can only be used once. If your opponent uses Charm, then White Herb will cure your Defense decrease right away. If you use Overheat, then White Herb will cure your Special Attack decrease right away. If Umbreon uses Curse six times and Baton Passes to you, then White Herb will cure your Speed decrease right away while keeping the Attack and Defense increases. It is handy in a couple of situations.
 Salac Berry, Petaya Berry, and Leichi Berry (RSE/FRLG, D/P only)
These items increase a certain stat by one stage when your health reaches 25%. Salac Berry increases Speed, Petaya Berry increases Special Attack, and Leichi Berry increases Attack. There are other berries that increase different stats, but those are usually not used so they will not be included.