Battle System

Battles are central to the Pokémon universe, and this system was designed to keep it clean and fun. Please keep in mind that this is a system designed specifically for roleplay. Strategies that might work in the games might not work on this site and vice versa.

Basics
This system is based in the rules set by the game.

Trainers can only carry 6 Pokémon in their party at a time.
Pokémon may only have 4 moves at one time.
Every Pokémon has 1 ability that cannot be changed except through evolution.
No items, except Mega Stones, can be used.
Natures are irrelevant.
In this battle system, there is little distinction between special/physical moves, attack, and defense except in special cases.

For the sake of balance, a character may only ever carry one Mega Stone in their possession.

While you can catch and own as many Pokémon as you desire, you can only use 9 as battlers (6 in party and 3 alternates in PC storage). This is necessary to prevent people from exploiting the system.

If an unresolved battle hasn't been posted in for 1 week, the last person to post is automatically declared the winner.

Tiers
Instead of levels, trainers are divided into broad categories known as tiers. These tiers indicate your skill level as a trainer and the strength of your Pokémon. The higher your tier, the stronger you are. Tiers both decide the HP of your Pokémon and the amount of damage they deal with each attack.

First Tier are low-level or beginner trainers.
Second Tier are advanced trainers, but aren't considered exceptional.
Third Tier are high-level trainers, capable of taking on a league challenge if they chose to.

First Tier: 80 HP
Second Tier: 160 HP
Third Tier: 200 HP

Anyone can move up a tier through enough hard work.

Damage
Attacks do damage that deduct an opponent's HP. When a Pokémon's HP is brought down to 0, they are no longer able to battle until healed. Each attack has a base power ascribed to it, which translates to damage. Use a resource such as PokémonDB to find a move's power.

p=Power
HP=Health deducted from an opponent

First Tier damage
10p - 2 HP
15p - 4 HP
20p - 6 HP
25p - 8 HP
30p - 10 HP
35p - 12 HP
40p - 14 HP
45p - 16 HP
50p - 18 HP
55p - 20 HP
60p - 22 HP
65p - 24 HP
70p - 26 HP
75p - 28 HP
80p - 30 HP
85p - 32 HP
90p - 34 HP
95p - 36 HP
100p - 38 HP
Anything higher - 48 HP
Self-Destruct/Explosion - 75 HP

Second Tier damage
10p - 4 HP
15p - 6 HP
20p - 8 HP
25p - 10 HP
30p - 12 HP
35p - 14 HP
40p - 16 HP
45p - 18 HP
50p - 20 HP
55p - 22 HP
60p - 24 HP
65p - 26 HP
70p - 28 HP
75p - 30 HP
80p - 32 HP
85p - 34 HP
90p - 36 HP
95p - 38 HP
100p - 40 HP
Anything higher - 50 HP
Self-Destruct/Explosion - 80 HP

Third Tier damage
10p - 8 HP
15p - 10 HP
20p - 12 HP
25p - 14 HP
30p - 16 HP
35p - 18 HP
40p - 20 HP
45p - 22 HP
50p - 24 HP
55p - 26 HP
60p - 28 HP
65p - 30 HP
70p - 32 HP
75p - 34 HP
80p - 36 HP
85p - 38 HP
90p - 40 HP
95p - 42 HP
100p - 44 HP
Anything higher - 54 HP
Self-Destruct/Explosion - 85 HP

Keep in mind that some moves have special effects (such as recoil or priority). Make sure to include these in your calculations.

Type Effectiveness
Each type has its weaknesses, strengths, and even immunities. This works much how you'd expect.

0x effectiveness does no damage (e.g. Normal against Ghost).
1/4 effectiveness does a quarter the usual damage (e.g. Poison against Ground/Rock).
1/2 effectiveness does half the usual damage (e.g. Water against Grass).
2x effectiveness does double the usual damage (e.g. Psychic against Fighting).
4x effectiveness does quadruple the usual damage (e.g. Fire against Bug/Steel).

Just simple multiplication. Round to the nearest whole number.

Status Effects
Certain moves and abilities can inflict negative conditions on an opponent.

Burn: Every turn, 10 HP is deducted. Power of attacks is not reduced.
Sleep: Roll the Status Dice. If you roll a 1 or 2, you stay asleep. If you roll a 3, you wake up. After 3 turns, if a Pokémon is still asleep, it automatically wakes up.
Paralysis: Roll the Status Dice. If you roll a 1, you are immobilized and cannot attack that turn. If you roll a 2 or 3, you attack. The speed of paralyzed Pokémon is cut in half. Paralysis disappears after 4 turns automatically.
Confusion: Roll the Status Dice. If you roll a 1, you inflict half of the damage of your intended attack on yourself. If you roll a 2 or 3, attack. Switching out will erase this ailment. Confusion disappears after 4 turns automatically.
Poison: Every turn, 10 HP is deducted.
Bad Poison: Every turn, 1/8 of max HP is deducted.
Infatuation: Roll the Status Dice. If you roll a 1 or 2, you are overcome with attraction and cannot attack that turn. If you roll a 3, attack. Fades if one of either Pokémon is switched out.
Frozen: Roll the Status Dice. If you roll a 1, you remain frozen. If you roll a 2 or 3, you are thawed out. Fire-type attacks used by another Pokémon will remove this status. After 3 turns, if a Pokémon is still frozen, it automatically thaws out.

If you use a move that has a chance of inflicting a status condition, roll the Chance Dice. If you roll a 1-5, nothing happens. If you roll a 6, they are inflicted with the status.

Healing Moves
All healing moves restore 40 HP. However, some may vary with special conditions.

Moonlight, Synthesis, and Morning Sun will restore 60 HP in sunny weather, 40 HP in normal conditions, and 20 HP in all other weather (such as rain or hail).

Swallow will restore 20 HP for every time the user has used Stockpile (up to three times).

'Attacking' moves that restore HP, such as Giga Drain or Absorb, will only restore half the HP inflicted on the opponent.

Multi-Strike Moves
For multi-strike moves, such as Bullet Seed or Tail Slap, roll the Chance Dice. If you roll a 1-2, you will hit twice. If you roll a 3-4, you will hit three times. If you roll a 5, you will hit four times. If you roll a 6, you will hit five times.

Accuracy
If an attack has less than 85 base accuracy, it may not hit.

If a move has 80-85 accuracy, roll the Chance Dice. If you roll a 1-2, it will miss. If you roll a 3-6, it will hit.
If a move has less than 80 accuracy, roll the Chance Dice. If you roll a 1-4, it will miss. If you roll a 5-6, it will hit.

OHKO moves, such as Fissure or Guillotine, have their own OHKO Dice. If you roll a 1-9, it will miss. If you roll a 10, it will hit.

Stat Changes
Certain moves can be used to boost or lower stats. Using this system, there is no differentiation between physical and special damage (i.e. for attack/special attack or defense/special defense).

Attack & Defense
You can not lower attack any lower than 4 stages.
-4 stages - -90% damage
-3 stages - -60% damage
-2 stages - -30% damage
-1 stage - -10% damage
Basic Attack - +0% damage
1 stage - +10% damage
2 stages - +30% damage
3 stages - +60% damage
4 stages - +90% damage
5 stages - +120% damage
You cannot raise attack any higher than 5 stages.

You cannot lower defense any lower than 5 stages.
-5 stages - +120% damage done by opponent
-4 stages - +90% damage done by opponent
-3 stages - +60% damage done by opponent
-2 stages - +30% damage done by opponent
-1 stage - +10% damage done by opponent
Basic Defense - -0% damage done by opponent
1 stage - -10% damage done by opponent.
2 stages - -30% damage done by opponent.
3 stages - -60% damage done by opponent.
4 stages - -90% damage done by opponent.
You cannot raise defense any higher than 4 stages.

Speed
Speed is the only base stat that is represented. The Pokémon with the higher base speed always moves first (except in special cases).

1 stage - Boosts a Pokemon's base speed by 50%.
2 stages - Boosts a Pokemon's base speed by 100%.
3 stages - Boosts a Pokemon's base speed by 150%.
You cannot raise speed any higher than 3 stages.

Accuracy & Evasion
Evasion or accuracy lowering moves don't work the same as other stat changing moves. You can only lower evasion or accuracy by one stage.

With evasion lowering moves, moves with 80-85 accuracy are now sure to hit.
For moves with less than 80 accuracy, use the Chance Dice. If you roll a 1-2, it will miss. If you roll a 3-6, it will hit.

With accuracy lowering moves, roll the Chance Dice.
If a move has over 85 accuracy, if you roll a 1-2, it will miss. If you roll a 3-6, it will hit.
If a move has 80-85 accuracy, if you roll a 1-3, it will miss. If you roll a 4-6, it will hit.
If a move has less than 80 accuracy, if you roll a 1-5, it will miss. If you roll a 6, it will hit.

Weather
Weather can make a significant impact on a battle, activating abilities, powering up moves, among other effects. These effects are the same as in the game, with just a few tweaks.

Hail will deduct 10 HP per turn from all non-Ice-type Pokémon.
Sandstorms will deduct 10 HP per turn from all non-Rock, non-Ground, and non-Steel-type Pokémon.

Make sure to implement the RP thread's weather into the battle.

Entry Hazards
Entry hazards are moves that cause a battlefield effect for all opposing Pokémon leaving their Pokéball to enter the match.

Spikes will deduct 10 HP in damage to grounded Pokémon entering the battle. Additional layers (up to 3 total) will stack on an additional 5 HP in damage.
Stealth Rock will deduct 10 HP in damage by default to Pokémon entering the battle. Pokémon that resist or are weak to Rock-type will receive different damage accordingly.
Sticky Web will lower the speed of grounded Pokémon entering the battle by one stage
Toxic Spikes will poison grounded Pokémon entering the battle. An additional layer will badly poison them. If a grounded Poison-type switches in, the hazard will be absorbed and its effect will be removed. Steel-types are immune.

Flinching
Some moves have a small probability of causing the opponent to flinch.

Roll the Chance Dice. If you roll a 1-5, the target won't flinch. If you roll a 6, the target will flinch.

Other moves (such as Fake Out) will guarantee a flinch, unless negated by an ability. These don't require the Chance Dice.

Critical Hits
Critical hits, in this battle system, can only be induced by a few certain moves (e.g. Storm Throw). If a move is listed with a high critical hit ratio, roll the Chance Dice when attacking. If you roll a 1-4, it will do normal damage. If you roll a 5-6, you will land a critical hit, which will do an additional +10 damage.

Mega Evolution
A Pokémon holding a Mega Stone can Mega Evolve. Pokémon can Mega Evolve and attack in the same turn. Mega Evolving will grant boosts to damage and speed. You can only carry one Mega Stone in your party at a given time, meaning only one of your Pokémon may Mega Evolve.

+50% damage
+20 points speed

Resources
PokémonDB is an excellent resource that I personally recommend, with all the information you need on Pokémon, moves, abilities, types, and more.

Credit and props to Jay for creating the original core battle system that this is built around. This wouldn't have come together without his hard work and ingenuity.