I've used Abomasnow few times before, and it's pretty decent, actually; with Snow Warning ability, it's able to summon hail as soon as it gets out of its Poké Ball, and this enables it to take some major advantage with moves such as Blizzard. Blizzard usually has very low chance of striking, unfortunately, but so long as you have hail on the field functioning correctly, it will not fail. If used correctly, Abomasnow is fantastic. Though, I have yet to give its mega-form a try. I did test it in-game a couple of times, but not competitively, sadly. I'm sure it's not bad, however.
What people usually tend to pair with this Pokémon, I believe, is Walrein. It has an ability (whose name I can't put my finger on at the moment, sorry to say) that heals its health every turn during hail, and if you give this Pokémon a set of Leftovers, it's able to recover even further, technically making it un-damageable, if you know what I mean. Have used it few times, and it has always managed to impress.
It'd be nice if they were to give Walrein a mega-evolution at some point in future, if possible. They're said to have seven unannounced megas in Omega Ruby and Alpha Sapphire right now, and perhaps this could be one of them? I feel that it'd be a nice plan to capitalize on; although Walrein might not be as popular among fans outside of competitive scene, it's still native to Hoenn, which is where these games take place.
