This is the big new battle gimmick (pun intended) introduced in Sword and Shield, replacing the Mega Evolutions from X and Y, as well as the Z-Moves from Sun and Moon. Basically, Pokémon become gigantic!
Prerequisite of Dynamax
With the exception of the 3 Legendary Pokémon unique to Galar, all Pokémon are capable of Dynamaxing. However, there are two specific conditions that must be met.
You must have a Dynamax Band. Actually, you'll get one very early on, so you don't need to worry about this.
There must a Power Spot nearby. Power Spots are commonly located in the very centre of Gym Stadiums, as well as Pokémon Dens.
Mechanically speaking, you can Dynamax during nearly every Gym Leader/Pokémon League battle, Max Raid Battles, plus a handful of story battles. You can also Dynamax during multiplayer battles.
If the conditions to Dynamax are met, you can Dynamax a Pokémon by selecting "Fight" and then pushing the big "Dynamax" button to the left of a Pokémon's moves (where the old Mega Evolution and Z-Move button would've been). Doing this will change all of the Pokémon's moves to the corresponding Max Moves. Now select a Max Move and you're good to go!
Pokémon will Dynamax at the very start of the turn, before any Pokémon can use their moves. If both trainers Dynamax at the same time, the Pokémon will the higher Speed stat will Dynamax first. Pokémon will remain Dynamaxed until 3 turns have passed, they are KO'd or they switch out. Similar to Mega Evolution, each trainer can only Dynamax once per battle.
Benefits of Dynamax
Obviously, Dynamax isn't just for show. Firstly, Pokémon have increased HP for the duration of Dynamax. You can also boost the amount of increased HP by feeding Pokémon Dynamax Candy, earned from winning Max Raid Battles. Also, Dynamaxed mons will not flinch. Combined, this makes Dynamaxed Pokémon more durable and resilient than normal.
In addition, Dynamaxing allows Pokémon to use extremely powerful Max Moves. These are similar to Z-Moves, in that they deal a lot more damage than usual. But that's not all--they also have very useful secondary effects. Some Max Moves can increase your team's stats or lower the enemy team's stats, while others can change the weather or terrain effect.
The Max Moves available to a Pokémon depend on the Type of the Pokémon's original moves. Meanwhile, the damage of a Max Move scales with the damage of the original move. Max Moves cannot miss and, like Z-Moves, they can partially bypass moves like Protect.
There's one exception to the rule: if the original move is a status move, it will always change into Max Guard, regardless of its Type. Max Guard works like Protect, but it will completely guard against even Max Moves.
|Normal||Max Strike||Reduces enemy team's Speed.|
|Fire||Max Flare||Triggers Sunny Day.|
|Water||Max Geyser||Triggers Rain Dance.|
|Grass||Max Overgrowth||Triggers Grassy Terrain|
|Electric||Max Lightning||Triggers Electric Terrain|
|Ice||Max Hailstorm||Triggers Hail.|
|Fighting||Max Knuckle||Boosts ally team's Attack.|
|Poison||Max Ooze||Boosts ally team's Special Attack.|
|Ground||Max Quake||Boosts ally team's Special Defence.|
|Flying||Max Airstream||Boosts ally team's Speed.|
|Psychic||Max Mindstorm||Triggers Psychic Terrain.|
|Bug||Max Flutterby||Reduces enemy team's Special Attack.|
|Rock||Max Rockfall||Triggers Sandstorm.|
|Ghost||Max Phantasm||Reduces enemy team's Defence.|
|Dragon||Max Wyrmwind||Reduces enemy team's Attack.|
|Dark||Max Darkness||Reduces enemy team's Special Defence.|
|Steel||Max Steelspike||Boosts ally team's Defence.|
|Fairy||Max Starfall||Triggers Misty Terrain.|