This should help:
Walrein@Leftovers
Modest/Bold nature
Ev's 252 Sp.Attack/Defense,6 HP
Surf
Ice Beam
Hidden Power:Electric
Encore/Protect
This one is made to stay on the game,with Leftovers you recover HP each turn,Protect might work with Leftovers but then there is Encore which is better that Protect,Ice Beam covers it's weakness that is Grass,Surf covers it's weakness Rock and they both gain Stab,Hidden Power:Electric is there so that you don't get stuck with other Water types.
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Walrein@Chesto Berry
Brave nature
Ev's 190 Sp.Attack,62 HP,152 Attack,106 Defense
Curse
Rest
Ice Beam/Surf
Earthquake/Double Edge/Rock Slide
Curse using Walrein is a huge threat as Curse raises Attack/Defense by 1 Point each use,Rest recovers all that lost HP,Ice Beam/Surf get Stab and cover it's weakness,Earthquake covers it's other weakness Electric and will do a lot of damage once it has 3/5 Times,then there is Rock Slide and Double Edge which are pretty strong.
Rock Slide kills Ice types.Double Edge is stronger than Earthquake but you get recoil damage,but that doesn't matter because by that time you probably have used Curse 4/5 Times.
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Walrein@Quick Claw
Brave/Quiet nature
Ev's 252 Attack/Sp.Attack,6 HP
Surf
IceBeam
Earthquake
Body Slam/Double Edge/Rock Slide
Mixed Walrein is good and with Quick Claw you may get more chances of Attacking first,Surf and Ice Beam get Stab,Earthquake covers it's weakness Electric and is quite Powerful.
Body Slam gives you a chance of Paralyzement but then Double Edge is Stronger,Rock Slide is for you not to get stuck with other Ice Types.
Body Slam/Power:85
Double Edge/Power:120
Rock Slide/Power:75
All of these attacks are very powerful so choose wisely!