>>31455631Yes to the Spd, yet to Light Ball being a Mega Stone.
No to the Atk loss, as Pikachu can go either physical or special, and its signature attack is a physical move.
Anyway, what I'd go with
Light Ball works as a Mega Stone
+20 Attack
+20 Sp Attack
+60 Speed
Ability: Lightning Surge - Electric Attacks damage Ground Types
As for design, pic is along the lines I'd go with. Best kept simple.
