The following details the major changes to Pokemon's battling mechanics that have occurred between each generation. Minor changes like alterations to a move's Base Power or a slight change in how an ability works usually will not be included, but differences in competitively relevant move mechanics (such as RBY's Hyper Beam, BW's Explosion nerf, etc.) are listed.
Changes from SM to ORAS
Changes from BW to DPP
Changes from SM to ORAS
- Burn damage is 1/8 per turn.
- Paralysis multiplies speed by 1/4.
- Confused Pokemon have a 50% chance of hitting themselves each time they try to move.
- Mega evolution happens after turn order is determined. For example, Mega Metagross's speed increase, Mega Swampert's Swift Swim, and Mega Sableye's lack of Prankster don't affect turn order on the turn they mega evolve.
- IVs are tied to Hidden Power type, so a Pokemon with any Hidden Power type other than Dark must have imperfect IVs.
- Dark void is 80% accurate and works regardless of the user's species.
- Destiny Bond does not fail from consecutive use.
- Gale Wings works regardless of the user's HP.
- Prankster-affected moves have no added immunities.
- The Base Power of the second hit of a Parental Bond-boosted attack is half of the attack's Base Power.
- Aerilate, Pixilate, and Refrigerate multiply the Base Power of affected attacks by 13/10, and Normalize does not change the Base Power of anything.
- Soul Dew multiplies the Special Attack of Latias and Latios by 3/2 instead of powering up certain types of attacks.
- Terrains and Mega Pokemon do not exist.
- Grass Pokemon are affected by "Powder" and "Spore" moves.
- Electric Pokemon can be paralyzed.
- The Fairy type doesn't exist, and the Togepi and Clefairy families are Normal-types.
- Steel resists Ghost and Dark.
- Critical hits multiply the damage by 2 instead of 3/2.
- Ghost Pokemon can be trapped.
- The Base Power of Knock Off is 20, and doesn't increase by knocking off items.
- The Base Power of Hidden Power varies from 31 to 70 due to IVs.
- Substitutes do not treat sound moves and Infiltrator-affected moves differently.
- Weather caused by Drizzle, Drought, Sand Stream, and Snow Warning last indefinitely.
- Oblivious only prevents infatuation and captivate.
Changes from BW to DPP
- Team Preview does not exist.
- A Pokemon's sleep counter does not reset when switching out. Also, sleep lasts for 1 to 4 turns rather than BW's 1 to 3.
- The moves Explosion and SelfDestruct temporarily halves the opponent's Defense, effectively doubling their Base Power.
- Wish heals the target by 50% of its HP, rather than 50% of the user's HP.
- The trapping effects of Mean Look can be Baton Passed.
- Taunt lasts for 2 to 4 turns.
- Encore lasts for 3 to 7 turns.
- Petal Dance, Thrash, and Outrage are paused but not disrupted if the user can't move due to sleep, freezing, or flinching.
- Crash damage is half of the damage the attack would have dealt, and half of the target's max HP if the target's type makes it immune to the attack.
- Tail glow raises the user's special attack by 2 stages.
- Growth does not raise Attack and is unaffected by weather.
- Tailwind lasts for 3 turns.
- Magic Coat does not affect switching moves, entry hazards, identifying moves, Disable, Spite, Encore, Torment, Taunt, Embargo, Heal Block, and Defog.
Sturdy does not prevent OHKOs from any moves except Horn Drill, Guillotine, Fissure, and Sheer Cold.
- Lightning Rod and Storm Drain don't grant immunities or raise Special Attack.
Soundproof Pokemon are immune to heal bell.
- When a Synchronize Pokemon gets badly poisoned, the opponent gets regular poison.
- Magic Guard Pokemon cannot be immobilized by paralysis.
- Mental Herbs can only cure infatuation.
- Choice items can lock a Pokemon into Trick or Switcheroo if both of the swapped items were Choice items.
- All Dark, Dragon, Electric, Fire, Grass, Ice, Psychic, and Water moves are special moves. All Bug, Fighting, Flying, Ghost, Ground, Normal, Poison, Rock, and Steel moves are physical moves.
- Sleep lasts for 1 to 6 turns. Sleep Talk will not always advance the sleep counter, as detailed here.
- When the faster Pokemon faints, the opposing Pokemon does not get to move.
- Taunt only lasts for 2 turns.
- Encore lasts for 2 to 6 turns.
- Counter and Mirror Coat treat Hidden Power as physical, regardless of type.
- When a Pokemon faints, it gets replaced before the next Pokemon moves. If all non-fainted Pokemon have already moved, then the fainted Pokemon gets replaced before the end of the turn.
- Thunder Wave does not activate Volt Absorb.
- Rough Skin damage is 1/16.
- IVs range from 0-15 rather than 0-31.
- A Pokemon can have 255 EVs in every stat.
- Natures and Abilities do not exist.
- If a badly poisoned Pokemon is switched out, it will be afflicted with regular poisoning.
- If a burned or poisoned Pokemon KOes its opponent, it will not take burn or poison damage that turn.
- A frozen Pokemon cannot attack on the turn it thaws out.
- If Sleep Talk chooses Rest, the Pokemon will regain all of its health and have its sleep counter reset. If Sleep Talk chooses Roar or Whirlwind and the user is faster than the opponent, it will fail. Sleep Talk always advances the sleep counter.
- Phazing moves, Counter, and Vital Throw must go second in order to succeed.
- Only one layer of Spikes can be set.
- Rather than Special Attack and Special Defense stats, Pokemon simply have a Special stat that functions as both.
- Items do not exist.
- Sleep lasts for 0 to 6 turns. Also, a Pokemon cannot attack on the turn it wakes up. A Pokemon using Rest will wake up after 2 turns rather than 3.
- If a Pokemon uses Rest while burned or paralyzed, it will retain the respective Attack or Speed drop until switching out. If a Pokemon uses an Attack or Speed boosting move while burned or paralyzed, respectively, the drops will be removed and the stat will raise as if no status was inflicted.
- The probability of critical hits is determined by base Speed. The formula used is %CH = Base Speed x 100/512. Critical hits ignore all stat changes for both Pokemon, as well as the effects of Light Screen and Reflect. They also double the Level of user during damage calculations, meaning they deal around 1.95x damage at Level 100, but closer 1.5x at Level 5.
- Bug is super effective against Poison and has normal effectiveness against Ghost, Poison is super effective against Bug, Ghost has no effect against Psychic, and Ice has normal effectiveness against Fire.
- If a Pokemon KOes an opposing Pokemon or breaks a Substitute with Hyper Beam, it does not have to recharge the next turn.
- A frozen Pokemon will not randomly thaw out.
- The accuracy and critical hit rate of all moves is reduced by 0.4% (except Swift, which will never miss).
- A poisoned or burned Pokemon loses 1/16 of its health rather than 1/8. Similarly, Leech Seed drains 1/16 of health rather than 1/8.
- A Pokemon hit by a partial trapping move cannot attack for the duration of the attack. However, it can switch out of the partial trapping move.
- Steel and Dark do not exist as types.
- Night Shade and Seismic Toss hit everything, regardless of type.
- If Explosion or SelfDestruct is used against a Pokemon behind a Substitute and breaks the Substitute, the user will not faint.
- Roar and Whirlwind have no effect.
- Haze removes major status conditions from the opponent.
- Pokemon are immune to secondary status effects from attacks of their type. So, Normal-type can't be paralyzed by Body Slam, Ice-types can't be frozen, etc.
- Counter misses if the last selected move's Base Power is 0, if the last move used by the opponent is not Normal- or Fighting-type (or is Counter), or if the last move used in battle (by either player) did no damage. Damage dealt is based on this move's damage, even if it was the Counter user who used it.