Abomasnow

Picture
Snow Warning - Summons permanent hail.

Type                                                                                                           Tier

Grass/Ice                                                                  BL

Base Stats

HP - 90
Attack - 92
Defense - 75
Speed - 60
Special Attack - 92
Special Defense - 85

Subseeder

Nature - Timid
Item - Leftovers
Moveset: Substitute                  EV Spread: 252 SpA/252 Spe/4 Atk
             Leech Seed
             Blizzard
             Focus Punch/Protect/Wood Hammer/Grass Knot

Probably the most used Abomasnow set, Abomasnow has its pros and cons compared other subseeders. Its ability, Snow Warning, takes away 6.25%, or 1/16, of a Pokemon's HP. If the Pokemon has Leftovers, it's effect is basically negated. Hail also gives Blizzard 100% accuracy, hitting other Grass types for super effective damage. Focus Punch knocks the daylights out of Blissey, Heatran, and Tyranitar. Another recommended move is Grass Knot/Wood Hammer as it takes care of Water types. This set gets walled by Steel types that take only neutral damage from Focus Punch. This points to Scizor, who can rip Abomasnow to shreds with Bullet Punch. Magnezone, too, can OHKO or 2KO Abomasnow with Flash Cannon and Signal Beam, respectively. However, it needs to watch out for Focus Punch as it can take out a large chunk of Magnezone's HP. You can also use the EV spread of 252 HP/4 SpA/252 SpD with a Sp. Def boosting nature, preferably Sassy or Calm. Careful is not a good choice as it lowers Abomasnow's Sp. Atk.


Swords Dance

Nature - Adamant
Item - Life Orb/Leftovers
Moveset: Swords Dance               EV Spread: 252 Atk/252 Spe/4HP
             Ice Shard/Ice Punch
             Wood Hammer/Seed Bomb
             Earthquake

Abomasnow's Attack may not wow you and its speed may be bad, the duo of Swords Dance and Ice Shard. After using SD once, Abomasnow's Attack becomes an extraordinary 622.  Ice Shard will go first unless the opponent uses a priority move and has a higher speed or the priority of the move (such as Protect) is higher. It can KO many Pokemon, most notably Flygon, Zapdos, and the commonly used Salamence. It also gains 2KO's on Rotom-H and Azelf. Ice Punch is there if you prefer power over speed. Wood Hammer takes care of Hippowdon and Suicune, as well as other Water, Ground, or Rock types such as Lanturn. If you don't like recoil damage, you can substitute Seed Bomb for Wood Hammer.
Earthquake takes out any Fire types not named Charizard, Moltres, or Ho-oh. It also makes short work of Magnezone and Lucario while providing an attack that can inflict a fair amount of damage to Scizor.

Paralysis works great for Abomasnow as it allows it to outspeed its opponents. Rotom-H can provide this and resists most types that Abomasnow is weak to. It also has Overheat, which can take out two of this set's biggest fears: Bronzong and Skarmory.

Choice Scarf

Nature - Hasty
Item - Choice Scarf
Moveset: Blizzard                  EV Spread: 140 Atk/116 SpA/252 Spe
             Wood Hammer
             Earthquake
             Hidden Power Fire/Focus Punch/Grass Knot/Energy Ball

With the Speed boost from a Choice Scarf, Abomasnow reaches a speed of 360, outspeeding Gengar and other threats like Salamence and Latias. Choice Scarf Magnezone is KO'd by Earthquake or HP Fire. Focus Punch can KO Blissey, but Wood Hammer will do a lot of damage to it anyway. When I mention Grass Knot, you know Energy Ball is going to be fighting for the slot as well. The choice is really up to you. Grass Knot obliterates heavy Water types like Walrein and Lapras, while Energy Ball can KO Vaporeon and Starmie with ease.
Scizor, yet again, is bad news for Abomasnow, so you can depend on Rotom-H or Rotom-F to help turn Scizor into mincemeat.

Choice Specs

Nature: Modest/Mild
Item: Choice Specs
Moveset: Blizzard                      EV Spread: 252 SpA/252 Spe/4 HP
             Grass Knot/Energy Ball
             Hidden Power Fire
             Focus Punch

With the boost from Choice Specs, Abomasnow's average Sp. Attack stat becomes fearsome. Blizzard is an obvious choice, while Grass Knot can be used on the majority of Water types due to most of them having a large amount of weight, but Energy Ball will help against things like Lanturn, Starmie, and Vaporeon. HP Fire can KO Scizor, Metagross and Forretress, but you need to watch out for Scizor and Metagross's Bullet Punch. Focus Punch allows you to 2 or 3KO Blissey, Snorlax, and Heatran. It will also have a good chance of OHKOing Tyranitar.

Counters

Scizor is an obvious choice; it pummels Abomasnow into the ground with Bullet Punch and U-Turn. Bronzong and Forretress will work decently with Gyro Ball, also since Abomasnow doesn't have much Speed either, it might not KO it. Metagross, and to a lesser extent, Jirachi, can take down Abomasnow with Meteor Mash and U-Turn/Psychic/Zen Headbutt, respectively. Most Fire Types can switch in on Abomasnow, but they need to watch for Earthquake if they aren't immune to it.