Let's create our own Z moves. Remember that they can only be used once per game making them similar to a type gem boosted move in BW.

My suggestions:

Pikachu
Corona Storm - Electric - 140 BP, special, never misses, breaks Protect and Detect, normal effective against Ground type

Shuckle
Comet Shower - Rock - 180 BP, physical, lowers target's speed by 1 stage
Snap - Bug - 40 BP, physical, Priority: +3, always flinches the target