Not that I care much for this discussion one way or the other but isn't there a massive difference between a Pokemon and a battle mechanic? I would think the Pokemon would be prioritized over a trinket based power up from a world tour narrative.
That being said unless they bring in megas in 9th generation and actually give 9th generation mega and Ash still exists (same with gens after 9), this series is Ash's only chance to use a mega.
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However I'm going to hate Ash getting a mega Lucario, look I'm not asking for an Ash-Greninja situation but I really fail to see why they couldn't give Lucario a 2nd mega evolution to showcase under Ash for uniqueness, as well as something new for 4th gen remakes but here we are, where the Pokemon company ultimately decided to cheapen the concept of remakes by just recreating the games with updated graphics and differences to the metagame due to fairy types and whatever else post 4th gen made to the games.
Sure they could have surprises up their sleeves but I'm expecting sheer disappointment, that the remakes feel unnecessary unless playing with fairy types and updated graphics is so necessary. Like I'd rather just play platinum than play the remakes. But its the fans fault for desiring remakes so badly. I feel more excitment for kids who never played the originals than I do with people who have and were expecting proper rdmakes rather than simple updated game.
The point is I'm bored of 6th generation Mega Lucario, and I'd rather they give Ash something not done to death. I already don't like Lucario's movepool of coursd they'll take the copout approach with Mega Lucario.
But "some" people hate "new things" and would rather Ash get the same boring stuff as everyone else because having some uniqueness to stand out is apparently overated. Like Ash-Greninja, some people would rather Ash just have your run of the mill everyday Greninja, because having the same thing over and over and over is somehiw "not" boring.
Pikachu already has the gigantamax form.
If you mean Ash using Gengar as his primary gigantamax Pokemon, I'd say no. At best Gengar would only use the form once and that's only if Ash chooses to "dynamax" Gengar because Pikachu isn't battling and the narrative sayx Ash uses the concept to battle his opponent.
But against Leon? No.