Walrein

Though hail is a more viable strategy in OU due to the presence of Abomasnow, Walrein is still a great candidate for hail in the lower tiers. With hail support from Snover, Walrein can easily stall out many powerful threats with just Protect and Substitute alone. Add in a generous helping of entry hazards and you will find Walrein to be one of the most difficult Pokemon to take out. Unless you have a specific Pokemon to counter Walrein, it won't be easy to defeat it, as passive damage can easily knock you out. While it's not going to be everywhere, it's definitely worth having some way to plow through this Pokemon when it rears its ugly head.