Thanks to AlphaWolf3312 for suggesting this mega.

Mega espeon keeps its psychic type, and it gains stats in sp attack, speed, sp defense and defense. It also gets the ability fur coat, halving damage from all physical attacks. After mega evolving it changed to have a thick, yet smooth fur coat and 3 tips on its tail. The red jewel on its head gets bigger to and its ears are folded back.
Stat boosts:
20 Speed
30 sp attack
20 defense
30 sp defense