Which main Pokémon games introduced Dynamax battles?

The main Pokémon games that introduced Dynamax battles are Pokémon Sword and Shield.

Released for Nintendo Switch on November 15, 2019, Sword and Shield introduced Dynamaxing as a signature battle mechanic of the Galar region. Once per battle, usually in special locations such as stadiums, a Pokémon can grow enormous for three turns. Its ordinary moves become stronger Max Moves, often with additional effects such as changing weather or setting terrain.

The related Gigantamax mechanic also debuted in these games. Gigantamaxing changes a Pokémon’s appearance as well as its size, and certain species gain a unique G-Max Move. Not every Pokémon can Gigantamax, while Dynamaxing is broadly available to eligible Pokémon in the main story and battles.

A common mix-up is confusing Dynamax with Mega Evolution or Z-Moves. Mega Evolution began in Pokémon X and Y, while Z-Moves debuted in Sun and Moon. Sword and Shield also used Dynamax Pokémon in cooperative Max Raid Battles, letting up to four players face powerful opponents together.