There are three types of Xatu: Offensive, Defensive, and Status. Remember that Xatu can switch safely into Lucario and Tyranitar, and proceed to ruin their lives without much consequence.
Offensive (Sweeper) Xatu
Modest, 252 SP.ATK, 252 SPD, 6 DEF
@Expert Belt
-Psychic
-Dark Pulse
-Hidden Power (Fighting)
-Heat Wave
This one is difficult to use, as Xatu's attacking power is only slightly above average, and he can't really OHKO anything. Best used against already-weakened opponents. Stealth Rock helps if you're going this route. Expert Belt is good for this Xatu as it has very good type coverage. However, there are better Special Sweepers out there, which is why I no longer use this one.
Defensive (Utility) Xatu
Timid, 252 DEF, 252 SPD, 6 DEF
@Light Clay
-Night Shade
-Reflect
-Light Screen
-Haze/Wish
Much better in competitive battling than the attacker variant, this Xatu needs no ATK EVs because its only offensive move is a fixed damage attack. Light Clay + walls gives 8 turns of protection. Choose Haze if you tend to run into a lot of boosting teams, and Wish in all other scenarios.
Status (Godly) Xatu
Timid, 252 DEF, 252 SPD, 6 DEF
@Flame Orb
-Night Shade
-Confuse Ray
-Trick
-Thunder Wave
My favorite one, and the Xatu I'm currently using. His game is to switch into Gyarados, Lucario, Tyranitar, etc. and inflict them with a 100% accurate Burn status via Trick, while simultaneously removing their Lum Berry/Choice item/Life Orb. After Xatu has ditched the Flame Orb, you can cause some more havoc with Confuse Ray/Thunder Wave.
Offensive (Sweeper) Xatu
Modest, 252 SP.ATK, 252 SPD, 6 DEF
@Expert Belt
-Psychic
-Dark Pulse
-Hidden Power (Fighting)
-Heat Wave
This one is difficult to use, as Xatu's attacking power is only slightly above average, and he can't really OHKO anything. Best used against already-weakened opponents. Stealth Rock helps if you're going this route. Expert Belt is good for this Xatu as it has very good type coverage. However, there are better Special Sweepers out there, which is why I no longer use this one.
Defensive (Utility) Xatu
Timid, 252 DEF, 252 SPD, 6 DEF
@Light Clay
-Night Shade
-Reflect
-Light Screen
-Haze/Wish
Much better in competitive battling than the attacker variant, this Xatu needs no ATK EVs because its only offensive move is a fixed damage attack. Light Clay + walls gives 8 turns of protection. Choose Haze if you tend to run into a lot of boosting teams, and Wish in all other scenarios.
Status (Godly) Xatu
Timid, 252 DEF, 252 SPD, 6 DEF
@Flame Orb
-Night Shade
-Confuse Ray
-Trick
-Thunder Wave
My favorite one, and the Xatu I'm currently using. His game is to switch into Gyarados, Lucario, Tyranitar, etc. and inflict them with a 100% accurate Burn status via Trick, while simultaneously removing their Lum Berry/Choice item/Life Orb. After Xatu has ditched the Flame Orb, you can cause some more havoc with Confuse Ray/Thunder Wave.