Mega Eevee’s design is pretty amazing. I would be amazed if GameFreak or anybody else could match the fun of priority switching between Eeveelutions. It is easily my favorite part of Pokemon Insurgence (which I think is amazing for a variety of other reasons too).
I was thinking Eevee could be further improved in a possibly not-too-complicated way by adding to the moves he can be tutored in to create more strategies for Mega Eevee. There is a great deal of untapped strategic versatility potential for Mega Eevee.
Taking from Eeveelution movesets, some suggestions to increase versatility are below. This would open a LOT more potential competitive sets to be run rather than just a unique mixed all-out attacker.
Additional Espeon Transformation Moves
Light Screen (utility option)
Reflect (utility option)
Calm Mind (boost option)
Additional Umbreon Transformation Moves
Nasty Plot (boost option)
Sucker Punch (priority option)
Additional Sylveon Transformation Moves
Draining Kiss (recovery option)
Additional Flareon Transformation Moves
Will-O-Wisp (strategic option)
Additional Galceon Transformation Moves
Ice Shard (priority option)
Additional Jolteon Transformation Moves
Thunderwave (strategic option)
Additional Leafeon Transformation Moves
Synthesis (recovery option)
Sword Dance (boost option)
However, in the hopes that my new favorite Mege evolution could be up there with Uber Megas, I would suggest allowing a post-Elite-4 (or further endgame) tutor to tutor Eevee in the partner Eevee moves, which are very cool and powerful and Eevee-themed.
Partner Evee Moves
|Bouncy Bubble|90|Water|Special| The user attacks by shooting water bubbles at the target. It then absorbs water and restores its HP by half the damage taken by the target.
|Buzzy Buzz|90|Electric|Special| The user shoots a jolt of electricity to attack the target. This also leaves the target with paralysis.
|Sizzly Slide|90|Fire|Physical| The user cloaks itself in fire and charges at the target. This also leaves the target with a burn.
|Glitzy Glow|90|Psychic|Special| The user bombards the target with telekinetic force. A wondrous wall of light is put up to weaken the power of the opposing Pokémon’s special moves. The original is physical, but would be bad for Espeon if so.
|Baddy Bad|90|Dark|Special| The user acts bad and attacks the target. A wondrous wall of light is put up to weaken the power of the opposing Pokémon’s physical moves.
|Sappy Seed|90|Grass|Physical| The user grows a gigantic stalk that scatters seeds to attack the target. The seeds drain the target’s HP every turn.
|Freezy Frost|90|Ice|Special| The user attacks with a crystal made of cold frozen haze. It eliminates every stat change among all the Pokémon engaged in battle.
|Sparkly Swirl|90|Fairy|Special| The user attacks the target by wrapping it with a whirlwind of an overpowering scent. This also heals all status conditions of the user’s party.