Pokémon Beginner's Guide

First of all, I will explain the origin of a Pokémon's individual stat in a particular ability (you probably know what a stat is already, right...):
Non-HP stat = ((Base stat * 2 + IV + EV/4) * Current Level / 100 + 5) * Nature modifier (truncate the decimal part of the calculated result)
HP stat = (Base stat * 2 + IV + EV/4) * Current Level / 100 + 10 + Current Level (truncate the decimal part of the calculated result)
So many beginners might ask, what is a base stat, what is an individual value (IV), what is a nature modifier, and what is an effort value (EV)... below I will define and explain these...
(1) Base stat:
As the name suggests, a base stat represents a fixed ability of a particular species (i.e., a type of Pokémon)... divided into HP, Attack, Defense, Speed, Special Attack, Special Defense... The higher a Pokémon's base stat, the stronger that Pokémon generally is... For example, when we say Aerodactyl is faster than Snorlax, we mean that Aerodactyl's speed base stat is higher than that of Snorlax... Base stats have a very large (arguably the greatest) effect on a Pokémon's abilities. For instance, for an offensive Deoxys... even if you max out its Defensive EVs and apply a nature modifier, it's impossible to make its Defense exceed its Attack. Generally, a Pokémon's base stats will be higher after evolution than before, but there are exceptions... For example, when a Trapinch evolves into Vibrava, the total base stat actually decreases... When a Scyther evolves into Scizor, the total base stat remains unchanged...
Here is a complete Pokémon base stat chart: Complete Pokémon Base Stat Chart
(2) Individual Value (IV):
Firstly... an IV is a completely random number... IVs, like base stats, are divided into 6 categories: HP, Attack, Defense, Speed, Special Attack, and Special Defense, with values ranging from 0 to 31... From the formula, it's clear that the higher the IV, the better the Pokémon's potential compared to its species... IVs are determined when you first encounter a Pokémon, and no matter how you train it afterwards, this value never changes... To illustrate, it's like how people have different natural strength levels... When we say we caught a 'perfect' Pokémon, it usually means that all of this Pokémon's IVs are high (of course, you need to be lucky to find one...) Unfortunately... IVs are hidden values in the game, and you can't see them without using a tool like the 'IV Checker' or some shameless cheat...Modding (this can all be fully modded to 31…) Apart from checking with such software… you can also use formulas to calculate… The specific formulas are as follows:
\Non-HP Individual Value = ((Stat / Nature Modifier - 5) * 100 / Current Level - 2 * Base Stat - Effort Value / 4)
\HP Individual Value = ((Stat - 10 - Level) * 100 / Current Level - 2 * Base Stat - Effort Value / 4)
\(Round down the fractional part of the above results and then add 1… actually this is just the reverse formula of the stat calculation formula…)
\(3) Nature Modifier
Nature also affects the stats of a Pokémon… it has 3 effects… no change, increases by 10%, decreases by 10%… The so-called perfect Pokémon mentioned above also considers the suitability of the nature modifier… Below is the nature modifier chart…
\Nature Modifier Chart:
\ Nature Attack Defense Sp. Atk Sp. Def Speed
(Lonely) △ ▼ - - -
(Stubborn) △ - ▼ - -
(Adamant) △ - - ▼ -
(Bold) △ - - - ▼
(TM) ▼ △ - - -
(Naughty) - △ ▼ - -
(Bashful) - △ - ▼ -
(Relaxed) - △ - - ▼
(Modest) ▼ - △ - -
(Calm) - ▼ △ - -
(Lax) - - △ ▼ -
(Quiet) - - △ - ▼
(Sassy) ▼ - - △ -
(Kind) - ▼ - △ -
(Careful) - - ▼ △ -
(Hasty) - - - △ ▼
(Timid) ▼ - - - △
(Jolly) - ▼ - - △
(Hardy) - - ▼ - △
(Serious) - - - - -
(Bold/Neutral) - - - - -
(Rash) - - - - -
(Quiet/Determined) - - - - -
▼ indicates multiplied by 09 times, △ indicates multiplied by 1.1 times.
Just like individual values, nature is also completely random…cannot be changed, cannot be inherited…But there is one difference…nature is not hidden, it can be seen when checking the PM's status…………
Therefore, when selecting a PM, first look at its nature…then consider individual values……
For example, a Lugia with maximum Special Defense IV of 31 and fully allocated Special Defense EVs (i.e., adding 252–255…actually 252 is enough…not wasting…I will explain what this means below……)……At level 100, with no nature adjustment, Special Defense is 407……With nature adjustment, it is 447…………A difference of 40……Even if the IV is at the most extreme value, the difference would only be 31……thus showing the importance of nature……
(4) Effort Values
Effort Values (EVs) are also divided into 6 categories: HP, Attack, Defense, Speed, Special Attack, and Special Defense…value range is 0–255…total across all 6 categories cannot exceed 510…From the formula, we can see…4 EV points equal 1 stat point…………Since the maximum EV for a category is 255…this means a fully EV-trained stat can be 63 points higher than a non-EV-trained stat (with nature adjustment, 69 points…)…showing their importance……Since 255/4 = 63.75…filling 255 EV points is effectively the same as 252 EV points………both giving a 63 stat increase…Thus, the total 510 EV points can fully cover 2 stats and add 1 point to a third stat (510 = 252*2 + 6)…
Unlike IVs…EVs are acquired later through training…obtained by battling or using items…When battling any PM, defeating it will yield EVs…the EVs gained depend on which PM is defeated, not on level or other factors…Once a PM gains EVs, they will be reflected in stat updates such as during leveling up (corresponding stats will increase)…If the PM is already at level 100 and EVs are not fully trained, the system can still update stats via certain actions like being deposited into the PC, but at level 100, battling PMs will no longer provide EVs (the system does not…).Your stat calculation won't be updated anymore, so make sure to complete your EV training before level 100. Of course, at this time using supplements is still possible (see details about supplements below)…

Here is a list of EV gains: Full Pokémon EV Gain Table

Now, let's talk about a method to earn EVs quickly… There is an item called the Exp. Vest (obtained after 4 consecutive wins at a house on Route 111) that doubles the EVs gained by the Pokémon holding the item after battle… However, the side effect is that the holder's Speed is halved in battle… Another one is the Pokérus… After being infected, a "PKRS" symbol appears in the status bar… It is called a virus and can spread to other Pokémon, but it is actually harmless and beneficial… Its effect is also to double the EVs gained after battle… After being infected, remember to let it spread to other Pokémon… Since this virus appears very rarely and disappears after a while (after disappearing there will be a black dot, indicating immunity, but the effect of doubling EV gain still remains)…

Also, the Macho Brace not only splits experience… but also allows the holder to gain the same EVs as the battle Pokémon… For example, fighting a Marill grants +2 HP EVs… The Pokémon in battle defeats a Marill and gains 2 HP EVs, and at the same time, a Pokémon holding the Macho Brace also gains 2 HP EVs…

Eating certain supplements can also increase EVs… But these supplements are very expensive (worth 9800… sold at the department store in Slateport City and the market in Rutile City…)

Specifically:
Protein: Attack EV +10
Iron: Defense EV +10
HP Up: HP EV +10
Calcium: Special Attack EV +10
Zinc: Special Defense EV +10
Carbos: Speed EV +10

Using ** to increase EVs is actually a shortcut… Unfortunately, you can only use up to 10 supplements per stat… That is, you can only add up to 100 EVs per stat through supplements… The remaining 155 points still need to be gained in battle… Moreover, these supplements are very expensive…

Also, EVs can be corrected if trained incorrectly… The method is as follows… Eating specific berries reduces corresponding EVs…

Pomeg Berry (21st Berry): Increases friendship by 3 or 6 but lowers HP EVs by 10 (Ruby/Sapphire only)
Kelpsy Berry (22nd Berry): Increases friendship by 3 or 6 but lowers Attack EVs by 10 (Ruby/Sapphire only)
Qualot Berry (23rd Berry): Increases friendship by 3 or 6, but lowers Defense EVs by 10 points (only in the Gold/Silver/Crystal versions)
Berry No. 24: Increases Friendship by 3 or 6 points, but lowers Special Attack EVs by 10 points (only in the Gold/Silver/Crystal versions)
Berry No. 25: Increases Friendship by 3 or 6 points, but lowers Special Defense EVs by 10 points (only in the Gold/Silver/Crystal versions)
Berry No. 26: Increases Friendship by 3 or 6 points, but lowers Speed EVs by 10 points (only in the Gold/Silver/Crystal versions)
Unfortunately, the EV-lowering effect is limited to the Gold/Silver/Crystal versions………………
Type Classification:
Special Attack Types: Fire, Water, Electric, Grass, Ice, Psychic, Dragon, Dark
Physical Attack Types: Normal, Fighting, Flying, Bug, Poison, Ground, Rock, Steel, Ghost
Dual-Type Analysis:
If a Pokémon has dual types… When it takes damage from one type, the type effectiveness is calculated as follows:
Type Effectiveness = First Type Modifier * Second Type Modifier
For example… Dragonite's types are Dragon + Flying… Dragon is weak to Ice… Flying is also weak to Ice… so Ice-type attacks deal 2 * 2 = 4 times type effectiveness damage to Dragonite
Gyarados' types are Dragon + Water… Dragon is weak to Ice, but Water resists Ice… so Ice-type attacks deal 2 * 0.5 = 1 times type effectiveness damage to Gyarados (which cancels out perfectly……)
Swampert's types are Water + Ground… Water is weak to Electric, but Ground is completely immune to Electric… so Electric-type attacks deal 2 * 0 = 0 times type effectiveness damage to Swampert…………