When you hear people talking in veiled whispers about actually using Ice-type Pokemon in OU, one of the few they'll be talking about is Mamoswine. Mamoswine's unique typing provides a neutrality to Stealth Rock, immunity to both hail and sandstorm, and an incredibly potent offensive STAB combination that is resisted only by Bronzong in all of DPP OU. This, in conjunction with Mamoswine's gigantic base 130 Attack stat, STAB Earthquake, and access to priority in the form of Ice Shard, leaves little to imagination as to how Mamoswine survives in a metagame so hostile to Ice-type Pokemon.
Mamoswine is a powerful Pokemon, but as an Ice-type, he carries all of their associated and unfortunate weaknesses. With the prevalence of Steel-, Fighting-, Water-, and Fire-type attacks in OU, a vast number of offensive Pokemon have the ability to outspeed and OHKO Mamoswine with one of their typical attacks. This makes it difficult to get Mamoswine into play, as his only free switch-ins are on predicted Electric-type attacks. As if to make matters worse, Mamoswine is cursed with very mediocre Speed, leaving him to be outsped by many common Pokemon in the tier. Despite these enormous setbacks, Mamoswine maintains his position as a moderate threat and potent wallbreaker.
This set is designed to do what Mamoswine does best: knock the stuffing out of things. With excellent type coverage and a base 130 Attack stat, opponents will constantly be playing a deadly guessing game of prediction in order to switch in something that can take Mamoswine's chosen attack. Although this set is very reliant on prediction, it yields an enormous payout if played correctly.
Mamoswine's Earthquake is the third-most powerful in the game, so there's no doubt that it'll be on this set. Despite its low Base Power, Ice Shard is a strong move that can snipe and eliminate the many Ice-weak Pokemon in OU. Stone Edge is Mamoswine's best option against Gyarados, and with a Choice Band can even OHKO physically defensive Zapdos after Stealth Rock damage. Superpower is an immensely powerful attack, chosen for an immediate OHKO on Blissey and to deal respectable damage to Bronzong and Skarmory switch-ins. Stealth Rock is useful on Mamoswine that carry Life Orb because he forces many switches with his power and can easily set it up.Team Options & Additional Comments >>>
Mamoswine makes for an effective lead with his excellent STAB attacking types, access to priority in Ice Shard, and Stealth Rock. Mamoswine's Attack stat and STAB Earthquake let him seriously hurt Metagross and OHKO Heatran leads through Shuca Berry. He can set up Stealth Rock reliably due to the switches he forces early in the match. Mamoswine can also function as a physical attacker later in the match with his excellent type coverage and powerful STAB priority.
Stealth Rock is an important asset for leads, and Mamoswine sets it up well with his usable Speed and offensive presence. Earthquake and Ice Shard are Mamoswine's STAB attacks on this set, providing him with a combination of high-power and priority for hitting hard and picking off faster leads, respectively. A couple of options exist for the last slot, all of which help in specific situations. Endeavor is recommended since he will often be taken down to 1 HP with his Focus Sash, allowing him to cripple an opposing Pokemon before ultimately being taken down. Stone Edge can be used over Endeavor as a more reliable means to deal with Gyarados switch-ins that will attempt to set up on Mamoswine.Team Options & Additional Comments >>>
Mamoswine has a few notable options that he can use to great effect and to beat his normal checks. When used in hail, Blizzard can be used off of Mamoswine's decent base 70 Special Attack stat with a Life Orb to 2HKO Skarmory. Bite can be useful for hurting Rotom-A and Azelf, although it is too weak to be useful anywhere else. An Expert Belt or NeverMeltIce is usable as an item to bluff the standard Choice Band set and score some surprise KOs against Pokemon that would normally love to set up on Choice-locked Earthquake, such as Zapdos, Gliscor, or Gyarados. Choice Scarf Mamoswine can be useful to catch your opponent off-guard with the added Speed. Because Mamoswine has access to STAB Ice Shard, however, it typically is in his best interest to run an item that boosts damage in some form. Mamoswine can also set up either Reflect or Light Screen as he forces a switch, but this role is generally better left to more durable Pokemon.
Mamoswine can run a set of Ice Shard, Earthquake, Endeavor, and either Substitute or Endure in the last slot to lure in and remove Pokemon that typically beat Mamoswine, such as Scizor and Bronzong. This set, when used with either a Liechi Berry or Salac Berry, can be effective due to Mamoswine's immunity to both hail and sandstorm, although it is easily foiled by phazing from the likes of Skarmory. Mamoswine is almost always better off using the Physical Attacker set instead and leaving the handling of Scizor and friends to other Pokemon that are better suited for it.
Checks and Counters
As an Ice-type Pokemon, Mamoswine has a rather unhealthy list of responses in the OU metagame. One of the things that makes Mamoswine viable in OU is that if the opponent mispredicts, they will likely lose a Pokemon due to Mamoswine's raw power and STAB type coverage. Jirachi, Lucario, and Scizor can all switch into an Ice-type attack and threaten to OHKO Mamoswine with their STAB attacks, but will be maimed by Earthquake if they mispredict. Similarly, Gyarados and Zapdos will try to switch into Earthquake and either set up on Mamoswine (in Gyarados's case) or attempt to seriously damage him with Heat Wave (in Zapdos's case). Levitate Bronzong is a textbook counter to anything Mamoswine will try to do, bar Choice Band Superpower. It shrugs off all of Mamoswine's other attacks and can take him down with a super effective Gyro Ball. Skarmory functions in a similar manner, despite having a neutrality to Ice-type attacks; he will set up Spikes on Mamoswine and then Whirlwind him away instead of trying to KO him. Because of Ice Shard's low Base Power, very defensive Pokemon that are weak to Ice-type attacks, such as Hippowdon and Celebi, can still check Mamoswine effectively. In addition, Cresselia and Uxie can set up dual screens on Mamoswine with their immunity to Earthquake and high defenses.