A powerful new mechanic known as Dynamax will make its debut in Pokémon Sword & Shield, and it involves JUMBO-SIZING YOUR POKÉMON!!
When a Pokémon is Dynamaxed, even small Pokémon become insanely huge, and all Dynamaxed Pokémon gain a powerful boost to their power for three turns. Only one of a Trainer’s Pokémon can become a Dynamax Pokémon per battle, so careful thought must be given as to when to activate the Dynamax.
While in a state of Dynamax, all of the Pokémon’s moves are upgraded to special Max Moves, which are powerful and may have additional effects, such as the Normal-type Max Strike lowering any target’s Speed stat. The Max Moves available are dependent upon the moves the Pokémon knew before entering Dynamax, and some moves may share a corresponding Max Move, as shown in the screenshot above.
It’s a phenomenon that is unique to certain locations in the Galar region and requires the Trainer to possess a Dynamax Band in order activate it. It can be activated during a battle similar to Mega Evolution in prior games, although not every location or battle may allow for a Dynamaxed Pokémon.
Thankfully the Gyms in the region are able to accommodate Dynamax Pokémon, as these epic matches make for excellent television across Galar.
More Screenshots of Dynamax in Action
More Milo and Dynamax Eldegoss 
Max Raid Battles
Dynamax also plays a very big role in Max Raid Battles, a four-player co-op battle against a wild Dynamax Pokémon inside of the Wild Area. Check out the Max Raid Battles page for more information and screenshots involving Dynamax in these battles.
Gigantamax
There’s a form beyond Dynamax that only certain Pokémon species are able to reach called Gigantamax. The specifics are currently unknown, but you can find out more about this phenomenon on the Gigantamax page.