* Mega Evolution is a mechanic that was introduced in Generation 6 (X and Y) and removed in Generation 8 (Sword and Shield). It's no longer a feature in the latest games.
However, you can still evolve Gardevoir into its final form, Mega Gardevoir:
1. Level up a Gardevoir to level 30. This is the standard evolution requirement for Gardevoir.
2. Learn the move "Mystical Fire". This can be taught through a variety of methods, including level-up, TMs, or breeding.
Once you have a Gardevoir that meets these criteria, it will mega evolve during battle if you have the Mega Stone: Gardevoirite.
Note: Mega Gardevoirite is a held item that was obtainable in Generation 6 and 7 games. It may be more difficult to obtain in later games depending on availability.
Let me know if you have any other Pokémon-related questions!