Assuming Sun and Moon has a new game mechanics that mega evolutions now have access to a fifth move that is not learned by level up, breeding and move tutor. What combinations would you like to see?
My ideas:

M-Blastoise: Shell Smash
M-Beedrill: Megahorn
M-Pidgeot: Focus Blast
M-Pinsir: ExtremeSpeed
M-Ampharos: Tail Glow
M-Banette: Recover
M-Steelix: Shift Gear
M-Sceptile: Draco Meteor
M-Audino: Recover
M-Gallade: Sacred Sword