I designed a mega evolution for Jolteon, he is based on Zeus, the Greek God of thunder!

Mega Jolteon-The Thunder Pokémon-Electric/Fighting. "Now able to use mega evolution, Jolteon is now able to harness the power of thunder, and is now able to take lightning from nearby storms and use it to attack enemies, though during mega evolution, it loses it's legs, but they return after mega evolution is over."