Pokémon Gen 2 streamlined the capture process and made it into something a lot more direct and easy to understand for the player. As such, the mechanics can be separated into 3 categories (Balls, Status, and HP) with each increasing the catch chance in different ways. It is important to note, however, that because a lot of bugs are present in the formulas used, some intended changes have no effect. The parts affected by such glitches are indicated. Finally, most of the data used is taken from the Gen II Capture Mechanics article on The Cave of Dragonflies.

Balls

Every Pokémon species has a fixed catch rate indicating how easily they can be caught. The lower the catch rate, the harder they are to capture. That catch rate is then increased depending on the Ball used. You can ask Kurt in Azalea Town to turn Apricorns found on Route 37, 42 and Azalea Town into special Balls. These special Balls have specific requirements that, if fulfilled, increase the catch rate significantly ; the catch rate is unchanged (x1) if unfulfilled. You can only pick up one of each Apricorn per day and the Ball-making process takes one day as well. In Gold and Silver, you can only give 1 Apricorn at a time, whereas in Crystal, you can give all your Apricorns of the same color at once.

Statuses

Some status effects can increase your final catch chance. Because the change is added at the end of the calculation, the increase is flat. There are only 2 statuses that increase the probability of a successful capture: Sleep and Freeze, with a 3.91% catch chance increase.

Hit Points

In Gen 2, lowering a wild Pokémon's HP increases the probability to catch a Pokémon significantly. The formula is based on the difference between max HP and current HP and is linear, which means any damage dealt increases catch chance by roughly the same amount. At 1 HP, you almost triple the base chance of capturing a Pokémon (without taking other factors into account).

List of glitches

• The Moon Ball multiplies by 4 the catch rate of Pokémon who evolve using Burn Heal instead of Moon Stone.
• The Fast Ball was supposed to increase the catch rate of all Pokémon that can flee, taken from 3 different tables (10% chance to flee, 50% chance to flee, always flees). It instead increases the catch rate of the first 3 Pokémon from the first table (Magnemite, Grimer and Tangela).
• In Crystal, the Heavy Ball misinterprets junk data, leading to wrongly increasing the catch rate of Kadabra, Tauros and Sunflora by 40.
• The Level Ball ignores the catching formula, nullifying any catching chance changes from Status and HP.
• The Love Ball requires the player Pokémon be the same species as the wild Pokémon, which is not clearly stated in the game, but working as intended. It also requires both Pokémon be of the same sex, which is clearly not working as intended.
• While the Burn, Poison and Paralysis statuses were supposed to increase the final catch chance by 5/256 (as opposed to the 10/256 for Sleep and Freeze), their associated check always fails, thus they have no effet on catch chance.

Catching strategy

As the general mechanics are simpler, so is the strategy used to catch Pokémon efficiently:

• Hit Points: Lowering a Pokémon's HP is always worth it and the most important. Use of the new move False Swipe is strongly recommended, as it cannot KO the target.
• Statuses: Putting a wild Pokémon to sleep is a flat 3.91% catch chance increase. Always make rare or legendary Pokémon sleep if possible. Against common Pokémon, the increase is marginal enough that you can ignore putting it to sleep. The best sleeping move is Spore (100% chance) but there are other moves such as Lovely Kiss and Sleep Powder (75% chance), Hypnosis (60% chance) or Sing (55% chance).
• Balls: Always use an Ultra Ball if possible. In order to save money, you can use a Great Ball or Poké Ball on more common Pokémon, as long as you lower their HP. There are only 4 Pokémon on which using a special Ball is worth it: Lugia (Heavy Ball, x7.67 catch rate increase), Snorlax (Heavy Ball, x2.6 catch rate increase), Golbat and Chansey (Friend Ball, starting Friendship set to 200).
• Extra: To prevent Pokémon from fleeing (like the Legendary Beasts), using a fast Pokémon with the move Mean Look is best.

Breeding

The probability of obtaining Pokémon Eggs is dependent on the species and the original trainer, and is rolled every 256 steps. In Gen 2 however, it is more difficult to get Eggs, as the probability goes from 31.25% with Pokémon from the same species and different trainers to 3.91% with Pokémon from different species and the same trainer. As you will probably use a Ditto to breed Pokémon, it is recommended that the Ditto be from another trainer to increase your chance of obtaining an Egg to 11.72%.

Experience boost

Using a Pokémon from different trainer grants a boost in combat equivalent to 50% of the gained experience. Since there are a lot of Pokémon to evolve as part of a Living Pokédex, catching Pokémon in a different version than the one used to level up Pokémon is a tremendous help for Pokémon who evolve at a level higher than 30 with a slow experience curve. Note that the missing experience needs to be significant enough to make up for the time lost trading.

Repel trick

The items Repel and Max Repel prevent random encounters from happening for Pokémon of a lower level than your first not-fainted Pokémon. Using one of these items while having the first active Pokémon be of a specific level can prevent specific Pokémon while retaining the ability to encounter ones of the same or higher level. A very useful trick to increase the encounter chance of rare Pokémon such as Chansey or the roaming Legendary Beasts.

Rare Candies

• Route 27 - Southeast of Tohjo Falls
• Route 28 - (Hidden) Northeast corner
• Route 34 - (Hidden) Fenced western area, north of the trees
• Violet City - Across the eastern lake
• Bell Tower - 5F, in front of the central pillar
• Glitter Lighthouse - 5F, east of the outer room
• Whirl Islands - (Hidden) B1F northeast, northeast of upper ladder
• Mt. Mortar - 2F, southwest corner
• Lake of Rage - End of western path, inaccessible on Wednesdays
• Vermilion City - Given by the Pokémon Fan Club Chairman
• Cinnabar Island - (Hidden) North of the island

HMs and important TMs

• HM 01 (Cut) - Ilex Forest
• HM 02 (Fly) - Cianwood City
• HM 03 (Surf) - Ecruteak City
• HM 04 (Strength) - Olivine City
• HM 05 (Flash) - Sprout Tower
• HM 06 (Whirlpool) - Team Rocket's Hideout
• HM 07 (Waterfall) - Ice Path
• TM 02 (Headbutt) - Ilex Forest → Goldenrod Department Store
• TM 08 (Rock Smash) - Route 36 → Goldenrod Department Store

Fishing rods

• Old Rod - Route 32
• Good Rod - Olivine City
• Super Rod - Route 12

The Mass Outbreak mechanic (also called Swarms) was introduced in Gen 2. Throughout the world, there are 6 extremely rare Pokémon. These Pokémon only appear in a single area (except for Qwilfish, appearing in 3 areas) and have a 1% encounter rate (except for Qwilfish and Remoraid, with 10%). Randomly every day, a trainer can call to warn you of a swarm of Pokémon, which means one of the 6 Pokémon now has an increased catch rate. In order for the trainer to call, you must have their number registered in the Pokégear. Only a single swarm can happen per day, and each swarm lasts until midnight.

Pokémon	Location	New rate	Swarm notifier	In Crystal
Marill	Mt. Mortar (entrance)	40%	Hiker Parry (Route 45)	No
Yanma	Route 35	30%	Bug Catcher Arnie (Route 35)	Yes
Dunsparce	Dark Cave (Route 31)	40%	Hiker Anthony (Route 33)	Yes
Snubbull	Route 38	30%	Schoolboy Chad (Route 38)	No
Qwilfish	Route 32	100%	Fisher Ralph (Route 32)	Yes
Remoraid	Route 44	100%	Fisher Wilton (Route 44)	No

In Gold and Silver, there are 2 categories of trees you can Headbutt, depending on your current location. Each category will always have the same encounter table, regardless of the area. In Crystal, the number of categories was increased to 6, with some categories only being accessible in a single area. For ease of access, all the Headbutt tree categories are in their own group in the catch locations page, with the C category being Crystal-exclusive.

• Headbutt tree A - Azalea Town, Ilex Forest, Lake of Rage, Route 26, 27, 34, 35, 36, 37, 38, 39
• Headbutt tree B - Route 29, 30, 31, 32, 33, 42, 43, 44
• Headbutt tree C1 - Azalea Town, Route 33, 42
• Headbutt tree C2 - Ilex Forest
• Headbutt tree C3 - Lake of Rage, Route 43
• Headbutt tree C4 - Route 26, 27, 32
• Headbutt tree C5 - Route 29, 30, 31, 34, 35, 36, 37, 38, 39
• Headbutt tree C6 - Route 44

Each category has 2 distinct tree rarities. The rarity of each tree is calculated based on your Trainer ID. Here is the link to a Headbutt Grid tool which allows you to determine the rarity of each tree by inputting your own ID.

While there are a lot of events unique to each day of the week, here is the list of the ones relevant to the Living Pokédex challenge:

Bug-Catching Contest

• Every Tuesday, Thursday and Saturday, you can enter the Bug-Catching Contest in the National Park.
• The goal is to catch the best Pokémon in the park. Only one Pokémon can be presented, and this Pokémon can be kept after the contest.
• The first place reward is a Sun Stone ; it is the only way to obtain it.
• Score is determined by a lot of factors, including stats and current HP. To get the best chance at winning, catch either a Scyther or Pinsir (preferably level 14) without damaging it while making sure Cooltrainer Nick is not participating (you can find him on the west side of the park).

Friendship

• The Pokémon Salon in Goldenrod Tunnel is open every day, except on Mondays.
• Every day between 3 and 4 PM, Daisy Oak in Pallet Town offers to groom one of your Pokémon.
• In Goldenrod City, in a house north of the Bike Shop, a woman can check the current Friendship value of the first Pokémon in the party. In order to evolve via Friendship, the value of the Pokémon needs to be 220, which corresponds to the message "I get the feeling that it really trusts you." (value between 200 and 249).

Other

• Every Monday, between 8 PM and 4 AM the next day, a Moon Stone can be obtained in the Mt. Moon Square.
• Every Friday, a unique Lapras appears in the water in Union Cave B2F.

Stones required to evolve Pokémon are a lot more difficult to obtain in Gen 2:

• Element Stones: On Route 25, Bill's grandfather gives you one stone of each type (and an Everstone) if you show him specific Pokémon.
• Moon Stone: You get one every Monday if you visit the Mt. Moon Square between 8 PM and 4 AM.
• Sun Stone: You need to place first in the Bug-Catching Contest.

Because the main way to get Element Stones was through Mystery Gift (a system using the GBC's infrared port), it is only possible to obtain one of each type in-game. Crystal introduced stones being given as victory rewards from specific trainers.

Still, because getting stones is so difficult and random, the only consistent way to evolve Pokémon in Gen 2 using stones is to temporarily trade them with a Gen 1 version, buy the required stone from the Celadon Department Store and use it.

The Mythical Pokémon Celebi is only obtainable in Crystal and is tied to a unique event which starts upon exiting the Goldenrod City Pokémon Center. How to trigger the event is different between the Virtual Console version or the cartridge.

• Virtual Console: The event becomes available once entering the Hall of Fame.
• Cartridge: The event was only available in Japan, yet has been localized. It is possible to unlock the event at any time by enabling the GameShark code 010B3CBE, saving then disabling the code.