Alakazam @ Alakazite
Ability: Magic Guard
EVs: 252 SpA / 4 SpD / 252 Spe
Modest/Timid Nature
IVs: 0 Atk
- Encore/Substitute
- Shadow Ball/Hidden Power Fire
- Psyshock/Psychic
- Focus Blast
With Alakazam, you'll want Magic Guard as it prevents you from taking entry hazard/sand damage before mega evolving, EVs are simple and obvious, you'll want to make sure Alakazam can as powerful and as fast as possible. Regarding the nature, Timid if you're using Zam on a Hyper Offensive team so it can outspeed Mega Lopunny, Mega Manetric, +1 DD Mega Altaria, etc, use Modest if you're running Balance with Thunder Wave support from Pokemon like Clefable, even with Modest you'll still be able to outspeed Pokemon like Scarf Ttar and +1 Mega Gyarados. For the moveset, Encore is one of Zam's best support moves as it can Encore Pokemon like Mega Altaria and Mega Zard into Dragon Dance and precede to 2HKO them, Substitute can be used to avoid Sucker Punches from Bisharp and status. Shadow Ball can be used to cripple Pokemon like Mega Metagross and the Lati twins, Psyshock can be used to hit Pokemon like Chansey for higher damage, while Psychic hits Landorus T, Gliscor and Rotom Wash harder, the choice is entirely team dependant. Lastly, we have Focus Blast to hit Steel types like Ferrothorn and Heatran and Dark types like Ttar and Bisharp, a move like Shadow Ball could be replaced with Hidden Power Fire only if your team struggles with Sp.D Sword Dance Scizor which can easily set on Mega Zam otherwise. I hope I've managed to help you :]