Walrein

As usual, the Ice-type is very much a mixed blessing. Ice-type attacks are always useful on a team, but the STAB boost on them comes with an unfortunate list of weaknesses. Stealth Rock hinders Walrein's ability to tank attacks, as taking 25% damage each time it comes in will wear it down fast. Even with these drawbacks considered, Walrein is a fine tank in OU play with handy resistances to Ice- and Water-type attacks and respectable offensive stats for a predominantly defensive Pokemon.

Back in ADV, the sight of Walrein in OU matches was rare, to say the least. However, with its cool new Ice Body ability, it can be a very useful--often integral--part of a hail-based team with support from Abomasnow. Walrein's stalling abilities with hail support are impressive and with Toxic or Toxic Spikes it can be surprisingly difficult to take down. Overall, Walrein got some very useful boosts in the transition from ADV to DPP, making it suitable for use in the OU environment.