This is the first time I've posted a moveset of my choice; hope I do alright!
Xerneas @Persim Berry/Babiri Berry
Ability: Fairy Aura
EV's: 208 Special Attack, 208 Attack, 48 Speed, 48 Special Defense
Nature: Hasty (raises speed, lowers defense), Strong willed/Somewhat vain/Strongly defiant/Hates to lose/Somewhat stubborn (slightly raises Special Defense)
Outrage/Megahorn/Close Combat (Coverage)
Psychic (coverage, protection against poison types)
Night Slash (coverage, high critical hit ratio)
Using this moveset could make fighting steel types a problem. This is when the Babiri Berry could be useful, to weaken the steel-type attacks. Then you could use Night Slash and hope for a critical hit. The Persim Berry could be used to recover from Outrage's confusion, so you could use it twice (getting a powerful, 4-6 turn attack).
I'm sure there are many loopholes and ways to get over this strategy; I'm still learning! I hope some of you find this useful! Please tell me if there are ways to make this moveset better!