"Pikachu-ite reacted with your Mega Ring! Pikachu evolved into Mega Pikachu!"

I imagine as nice as the form is, the trade off would be more power and slightly lower speed to compensate for higher power, kind of like Trunk's buffed out Super Saiyan form where he lost a lot of speed in trade for power.

Otherwise, this looks pretty good for an idea of an overly buff Pikachu ready to fight. Also kind of reminds me of the time SSBB skin swaps happened and Ganonchu (Ganondof model + Pikachu skin) happened. Looks well done. :D