Is there a particular reason why people are talking about Hyper Voice on Mega Altaria rather than Return? By the looks of it, Altaria's Attack stat is going to be the main boosted stat, so it sounds like it'll be higher than its Special Attack. Combine that with the fact that Return has a naturally higher base power and it just looks like it'll be the overall better option. Running physically-based Mega Altaria with Return also has the advantage of getting great neutral coverage with Earthquake, although I suppose Fire Blast works well alongside Hyper Voice. I guess the ability to bypass Substitutes is cool and all, but I'd honestly prefer Return overall.