The MEGA Dream ex subset largely contains reprints of various notable Pokémon and Trainer cards released in 2024 and 2025, including reprints of Pokémon ex, Tera Pokémon ex and Mega Evolution Pokémon ex cards. This set also debuts many new Mega Evolution Pokémon and characters introduced in Pokémon Legends: Z-A, such as Mega Dragonite and Mega Eelektross as Mega Evolution Pokémon ex and Canari as a Supporter card. It also introduces a new Mirror Holofoil Energy pattern and various Poké Ball patterns that can appear on Pokémon cards. Trainer's Pokémon and Mythical Pokémon can have a Mirror Holofoil featuring a regular Poké Ball, and most other Pokémon feature one of a Friend Ball, Love Ball, Dusk Ball, or Quick Ball. Mirror Holofoil Team Rocket's Pokémon feature the Team Rocket logo instead of a Poké Ball, but are still eligible to have an Energy symbol pattern.

Each sealed Japanese Mega Dream ex boster Box contains 10 booster packs containing 10 random cards each.