Here's why:
* Mewtwo is not a recruitable Pokémon: In these games, Mewtwo isn't a Pokémon you can encounter and befriend during your adventure. It's not included in the game's roster of recruitable Pokémon.
* Wonder Mail codes are primarily for events: Wonder Mail codes in these games are usually used for limited-time events, offering special items, Pokémon, or other bonuses. They are not meant to bypass the game's regular mechanics.
If you're looking to experience the power of Mewtwo in the *Explorers* series, you'll likely need to consider using a cheat device or playing a different *Pokémon Mystery Dungeon* game where Mewtwo is available.