- Mega Evolutions were introduced. A Pokemon that Mega Evolves will move when its base form would move that turn.
- - Pursuit has a strange interaction with Mega Evolution. Normally, all switches are resolved, and then Mega Evolution occurs. If a Pokemon uses Pursuit on a switching Pokemon, Pursuit will happen before all Mega Evolutions. If a Pokemon Mega Evolves and uses Pursuit, first the switch message will play, then the Pokemon will Mega Evolve, then Pursuit will be used, then the switch happens (if the target wasn't knocked out), then other Mega Evolutions happen.
- - Mega Stones cannot be given to or removed from a compatible Pokemon. They can be passed around to incompatible Pokemon - for example, Knock Off will fail to remove Kangaskhan's Kangaskhanite, but Knock Off will remove the same Kangaskhanite held by a Pikachu.
- Fairy Type was introduced. It hits Dragon, Dark, and Fighting super effective. It is resisted by Fire, Poison, and Steel. It resists Bug, Dark, and Fighting, and is immune to Dragon. It is weak to Poison and Steel.
- Steel no longer resists Dark and Ghost.
- Several special moves received slight nerfs to their base power.
- Assault Vest and Safety Goggles were introduced in this generation.
- Mail items were removed in this generation.
- Electric types are now immune to paralysis, and Grass types, Pokemon with the Overcoat ability, and Pokemon holding Safety Goggles are now immune to powder moves such as Spore and Rage Powder.
- Pokemon with the ability Oblivious are now immune to Taunt.
- Drizzle, Drought, Sand Stream, and Snow Warning now only set weather for five turns. Damp Rock etc. will increase that time to eight turns.
- Follow Me and Rage Powder now have a priority of 2, as opposed to 3 in previous generations.
- Electric, Grassy, and Misty Terrain were introduced in this generation. (Nobody except
Fangame10 uses them.)
- Hidden Power's base power is now locked to 60.
- Diancie's signature move, Diamond Storm, has a 50% chance of boosting its Defense by one stage for each Pokemon it hits.
- Sleeping Pokemon in this generation (and all future generations) sleep for 1-3 turns before waking up, and the timer does not reset when switching out.
- Paralysis reduces Speed by 75%.
- Confusion's self-hit chance is 1/2.
- Starting in this generation, Protect only has a 1/3 chance of succeeding when used consecutively. See "The Protect Counter" below.