There's no need for both Psychic and Night Shade on Xatu, since they function differently. Psychic is used as Xatu's STAB move, while Night Shade is used for inflicting more consistent damage, since uninvested base 95 Special Attack is somewhat weak. Replace one of them, as well as Protect, with Roost (for recovery) and U-turn (to serve as a scouting option). Depending on which offensive move you opt for, use a Calm nature with Psychic and a Careful nature for Night Shade (change the EV spread to 252 HP/4 Def/252 SDef to suit the nature change).
Relaxed is the preferred nature if you intend to use Dragon Tail on Blastoise, as Dragon Tail with a Relaxed nature breaks Kingdra's Substitutes.
Zap Cannon is annoyingly inaccurate and shouldn't see use on Eelektross. Also, Eelektross gained a lot of good B2/W2 tutor moves:
-Thunderbolt
-Flamethrower
-Giga Drain/Grass Knot
-Superpower/Hidden Power (Ice)
Nature: Quiet/Modest
EVs: 252 HP/252 SAtk/4 SDef
Item: Life Orb/Leftovers/Expert Belt
or
-Coil
-ThunderPunch
-Drain Punch
-Aqua Tail/Dragon Tail
Nature: Adamant
EVs: 252 HP/16 Atk/240 SDef
Item: Leftovers
Or you can consider Raikou, who's faster than Eelektross:
-Substitute
-Calm Mind
-Thunderbolt
-Hidden Power (Ice)
Nature: Timid
EVs: 4 Def/252 SAtk/252 Spe
Item: Leftovers
or
-Thunderbolt
-Hidden Power (Grass/Ice)
-Extrasensory
-Calm Mind/Volt Switch
Nature: Timid
EVs: 4 Def/252 SAtk/252 Spe
Item: Life Orb
or
-Thunderbolt
-Volt Switch
-Hidden Power (Ice/Grass)
-Extrasensory
Nature: Timid
EVs: 4 Def/252 SAtk/252 Spe
Item: Choice Specs
or
-Thunderbolt
-Volt Switch
-Hidden Power (Ice)
-Aura Sphere/Extrasensory
Nature: Rash/Timid
EVs: 4 Def/252 SAtk/252 Spe
Item: Choice Scarf