I know it's early but my theoretical Mega Glalie set (presuming it IS HP 80 ATK 120 DEF 80 Sp.atk 120 Sp.def 80 Spd 100)
Glalie @ Glalieite
Ability: Ice Body
EVs: 64 HP / 252 Atk / 192 Spe
Adamant Nature
- Icy Wind/Bulldoze
- Return
- Explosion
- Earthquake/Protect
allows it to outspeed Greninja after one Icy Wind/Buldoze (depends on whether you want to do more damage with bulldoze or ensure the speed drop with icy wind since it hits all types), Return will hit like a truck, EQ for coverage or possibly Protect so that you dont have to worry about being out-sped by anything due to the 80 base speed of regular Glalie
After rocks I think Explosion OHKOs Skarm and pretty much obliterates everything
Glalie @ Glalieite
Ability: Ice Body
EVs: 64 HP / 252 Atk / 192 Spe
Adamant Nature
- Icy Wind/Bulldoze
- Return
- Explosion
- Earthquake/Protect
allows it to outspeed Greninja after one Icy Wind/Buldoze (depends on whether you want to do more damage with bulldoze or ensure the speed drop with icy wind since it hits all types), Return will hit like a truck, EQ for coverage or possibly Protect so that you dont have to worry about being out-sped by anything due to the 80 base speed of regular Glalie
After rocks I think Explosion OHKOs Skarm and pretty much obliterates everything