Dragon Dance lets Altaria set up by boosting its Attack and letting it reach a good Speed tier.
Return at max Friendship is 102 Power; combined with Pixilate boosting it by 20% and making it Fairy-type, it's Altaria's overall best attacking option. However, since physical attackers are weak to burns, Facade can be used to ignore such effects while also being a lot more powerful than Return when statused.
Earthquake is generally more preferred and hits Steel and Poison types super effectively, but Fire Blast can be used to deal with threats like Scizor while also not having to worry about being burned.
Roost is used to keep Altaria healthy, especially since it boasts a respectable bulk.
Other details
Altarianite allows a much needed Mega Evolution for Altaria. Altaria's pre-Mega Dragon/Flying type also lets it freely switch into Grass and Ground-type moves.
Natural Cure is used but it will likely not serve much purpose as Altaria is likely to be immediately Mega Evolved after switching in.
From the pvpaltaria-yapedition tag
More Altaria-Mega sets
This is the only community set for Altaria-Mega so far.