The Strongest in History! Mewtwo Max Voltage!! (Japanese: ジ史上最強！ ミュウツーマックスボルテージ！！) is the third set in the Pokémon Tretta Ultimate Z series, and the twenty-first overall. It features 48 Tretta.
This set features the Genetic Pokémon Mewtwo as an Ultimate-class Tretta, which can use its signature movePsystrike and can Mega Evolve into Mega Mewtwo Y. Mewtwo also has a Z Tretta ability that will activate when it faces an opposing team containing at least 1 strong or very strong Pokémon (typically Master-class Tretta and above). This ability will boost Mewtwo's Fervor to "Max Voltage", increasing its stats to a larger extent than that of Pokémon in "Best Condition" or "Good Condition". While in this state, Mewtwo will glow with a purple aura.
Two special Origin-class Tretta were included in this set in commemoration of the 20th Anniversary of Pokémon Red and Green, which were released on February 27, 1996 in Japan. These Tretta come in a color mimicking that of the original Game Boy and have illustrations that pay homage to the original box art of Pokémon Red and Green. These Tretta are effectively treated as secret Tretta, featuring a collection number of Z3-??, and having a low encounter rate in the main game.
Arceus from Judgment! Arceus Advent is included in this set as the re-issued Ultimate-class Tretta, while Rayquaza is once again featured as a Legend-class Tretta with the ability to Mega Evolve. A handful of other Legendary Pokémon are included in The Strongest in History! Mewtwo Max Voltage!! as Master-class Tretta. All include pairs of Pokémon that form part of a Legendary trio and all have a Z Tretta ability that allows them to summon either the other member of the pair if used alone in Battle Mode, or the third member of the trio when used together. Xerneas and Yveltal will always summon Zygarde when used together, Reshiram and Zekrom will always summon Kyurem when used together, Dialga and Palkia will always summon Giratina in its Origin Forme when used together, and Primal Groudon and Primal Kyogre will always summon Rayquaza when used together. Legendary birdsArticuno, Zapdos, and Moltres also appear as Hyper-class Tretta with the Z Tretta ability. Each member of the trio can summon either of the other two members if used in Battle Mode, but will always summon Lugia if all three are used together.
The Strongest in History! Mewtwo Max Voltage!! marks the return of Tretta with the Form Change mechanic, with Keldeo able to change into its Resolute Form and Meloetta able to change into its Pirouette Form. In addition to Mewtwo and Rayquaza, this set includes 10 other returning Pokémon capable of Mega Evolution. All regular Tretta in this set are colored Prussian blue.
Search Mode includes locations with spring theme. The Field and Foot locations respectively replace Cave and Park from the previous set.
Challenge Battle includes five new Trainers to battle, including 1 new Trainer class. This new class sees Tretta Idol Hitomi form an Idol Unit with newcomer Sayoko as one of two 5-star challengers, a first for the game mode. Due to the inclusion of two 5-star challengers, the difficulty rating jumps from 2-star straight to 4-star when played in order. Players with Tretta Reports could also add the Legendary Sky High Pokémon Rayquaza to their Extra Attacker roster through repeated play.