- There are three new Pokémon battles; the Symbiose Battle, the Horde Battle and the Aligned Horde Battle.
- Symbiose Battle: Each two trainers use two Pokémon joining up into one, combining Total HP and portions of Stats, and can perform two moves at a time. The two Pokémon's Types and Ability will combines but won't stack with, making a total of 4 Types and two Abilities. Since two Pokémon have their energy connected and are together, they are threated as they are only one Pokémon. Also, Super Effective and Not Very Effective damage values are halved (X1.5 and X0.75, respectively) and Critical Hit damage modification is also halved. Certain Moves and Abilities are changed during Symbiose Battle. It is possible for the duo-Pokémon to Mega Evolutionate as both can hold different Holdable Items (Certain Items do not stack and others have less intense effect in Symbiose Battle) but both must be able to Mega Evolve and must hold a respective Mega Stones. The rest of battle mechanics remains unchanged.
New Mega, Champion & Primal Pokémon
Notice that certain Pokémon have two Mega Evolutions, and that the Champion Crystal are obtained only as the first place reward for the EXtreme Tournament. Pokémon in italian text were DLC from Mighty and Nasty Versions.
- Mega Foxature Mighty/Nasty (Grass/Fairy, Grass/Water)
- Mega Volcasaur Red/Green (Fire/Dark, Fire/Grass)
- Mega Grepapa Black/White (Water/Ground, Water/Fire)
- Mega Meganium Y (Grass/Fairy, Mega Meganium X is from Sunburn and Frostbite versions)
- Mega Swampert X (Water/Ground, Mega Swampert Y is the same from Omega Ruby and Alpha Sapphire)
- Mega Infernape Y (Fire/Fighting, the X one is the same from Sunburn and Frostbite)
- Mega Serperior X (Grass/Dragon, the Y one is the same from Sunburn and Frostbite)
- Mega Greninja Y (Water/Dark, the X one is from Sunburn and Frostbite)
- Primal Thuggler (Steel/Poison)
- Primal Toxihost (Ghost/Fighting)
- Mega Porygon-Z (Normal/Robot)
- Mega Gearclops (Light/Steel)
- Mega Golduck X (Water)
- Mega Golduck Y (Water/Psychic)
- Mega Excadrill (Ground/Steel)
- Mega Mr.Mime (Psychic/Fairy)
- Champion Magmortar (Fire/Light)
- Champion Electivire (Electric/Fighting)
- Champion Rhyperior (Ground/Steel)
- Champion Porygon-Z (Normal/Robot)
- Champion Butterfree (Bug/Fairy)
- Champion Beedrill (Bug/Poison)
- Champion Throh (Fighting)
- Champion Sawk (Fighting)
- Champion Umo (Fighting)
Some moves like Quiver Dance and Scald are changed for game balance or other reasons.
Like moves, abilities like Blaze variations are changed for mentionned reasons. The most notable changed Ability is Speed Boost mainly because of Blaziken and how cheap the ability itself is.
Other New/Changed Mechanics
- Does to Mega Ring absence, a new requirement involving level will be needed for Mega Evolving. Such required level is 40 to 80, depended on the Pokémon's total base stat. (For instance, to Mega Evolve a Zosteroark, it must have Level 70 unlike Zoroark who needs Level 50.)
- Mega Evolved Pokémon are nerfed; upon Mega Evolved or switched in as a Mega Pokémon, it starts with -1 Stage change for Attack, Defense, Sp.Attack, Sp.Defense and/or Speed, if any of it had already raised.
- For game balance, some Abilities such as Parantal Bond also disabled upon same circonstances, and will not be avaliable until 1 or 2 turns depended on it's competative uses (or three if it is a Legendary), while Mega Richeyes S being an exception, as it's Ability activates upon Mega Evolving and takes one more turn afterward.
- In the new EX Rules 2, if the Mega Evolved Pokémon's HP is at 25% (40% for Legendaries, 75% for Blaziken for game balance), it will Mega Devolve into it's normal forme, and cannot Mega Evolve again unless if it's HP becomes 100% again. There is also a Light-Type called Anti-Mega Beam which Mega Devolve both Pokémon in Mega formes and seal their Mega Stones until switched out.
- Certain Moves can be upgraded (term is Mega-Upgrade) by Mega Evolving, improving the first compatible move by enhancing the secondary effect or add another effect. Only one Move can be Mega-Upgraded at a time.
- Pokemon Staduim EX is rumored to include the most Pokémon avaliable, and possibly introduces the most Mega Evolution. The DLC Pokémon from previous games are also included.
- The semi-sequel of Mighty & Nasty is the DLC Pack "Second Quest", making these games the first Two-Versions games to be avaliable for a hardware.