Where would Castform land if he got a mega with an ability that combines Prankster and Forecast (Weather Alert?), and the 100 points were primarily in sp atk + spd?

This theoretically gets it to something like 70/70/80/120/80/100.

Maybe the ability only works on weather setting.

Alternatively: they add signature moves where castform can both set the weather and do like a 60 BP attack of that type.

I love this guy but there are so few reasons to run him.