Gardevoir

Mega Gardevoir sets itself apart from other Fairy-type threats like Tapu Lele with its access to Pixilate-boosted Hyper Voice and Trick Room. These moves allow Mega Gardevoir to function as an offensive Trick Room user that can simultaneously apply pressure to two foes.

Mega Gardevoir's ability to threaten problematic foes to Trick Room teams like Amoonguss also differentiates it from other Trick Room users like Cresselia and Mimikyu.

Mega Gardevoir is also capable of providing unique team support. Trace copies foes' abilities, and this can come in handy against foes like Landorus-T and Salamence, or scouting foes' abilities. The moveset can also be adjusted to employ utility moves like Will-O-Wisp, Taunt, and Destiny Bond.

As a Trick Room user, Mega Gardevoir's low physical bulk and high Speed can be detrimental. Mega Gardevoir is easily overwhelmed by a myriad of common physical attackers even when running bulk investment, and it is slower than foes like Tapu Bulu and Porygon2 under Trick Room. This leaves Mega Gardevoir somewhat reliant on its teammates to effectively function, and this combines with the fact that Mega Gardevoir takes up a Mega slot to make it somewhat of a Pokemon that must be built around.

Gardevoir has little to do against Steel-types like Mega Metagross, Aegislash, Heatran, and Ferrothorn due to them resisting its STAB combination.

While Mega Gardevoir may seem to be able to run a fast, offensive attacker set, its susceptibility to priority moves and the presence of faster threats like Kartana, Tapu Koko, and Mega Gengar make any sets other than Trick Room hard to justify over other threats like Tapu Lele.