The only practical use in OU (Pokebank) that I found for mega-Abomasnow is with the following core team: Mega-Abomasnow works really well in synergy with avalugg and tentacruel.
Avalugg is a good rapid spinner and has the best defense in the game + ice body (regen life when hail is on), add it leftovers/recover and this thing is impossible to kill (physically) when it hails. With maxed defense you can even resists quite well super effective physical attacks from physical sweepers.
Then you need a SpD wall, and Tentacruel is a good choice, the only thing that bothers me is that it takes damages from the hail, so the best would be a special defense wall that resists hail and fire (if you have an idea please let me know).
Tentacruel can also rapid spin, and with black sludge and the threat of scald it can do a good job against those fire types (as well as walls with toxic).
So it goes like this, you set the hail with mega-abo against a pokemon that doesn't represent a threat for him, on the switch you can go for leech seed/blizzard/substitute/giga drain they are all good depending on the situation, on the opponent switch, whatever you'll face you'll almost always have a good response: avalugg and tentacruel can both rapid spin/toxic or hit quite hard (114 base attack with avalugg is not something that you can ignore).
You can keep switching like this, set hail again, throw some spikes and rapid spin to be able to switch.
For everything that beat this core you still have 3 others available slots in your team, one pokemon with stealth rock would be a good thing. With so much residual damages the sweepers in your team will be able to do tremendous damages.
I think that this has huge potential, notice that tentacruel can be incredibly annoying on the switch with knock off, when you knock off some leftovers the opponent really feels the hail.
I've only been experimenting for a few matches but I think I got something really strong here.
Here is the very first match I did with this core, my opponent is quite strong (1900) but I think that he may have been experimenting too:
http://pokemonshowdown.com/replay/pokebankoubeta-61697821
You can see how exceptionally resilient Avalugg is under the hail, it is a very fun match but you gotta understand that this team is even more strong when aerodactyl can do is job correctly (damn magic bounce)
Let me know what you think about this synergy and sorry if I made mistake I'm not a native english speaker.
The concept is that with so much residuals damage I can sweep with some "unusual" sweeper, basically I use two bulky sweepers that are very resilient.
EDIT:
Just another brief replay to show that Avalugg is actually a very nice counter to common prankster such as Gliscor or Klefki. Abomasnow really shines in this battle.
http://pokemonshowdown.com/replay/pokebankoubeta-61739874
However this team remain quite weak against electric special attackers and is really annoyed by sableye so there is still a lot of work to do, maybe replace Dragonite with Heatran or find another special defense wall.
Here is the full team:
---- CORE ----
Abomasnow (M) @ Abomasite
Ability: Snow Warning
EVs: 252 SDef / 248 HP / 8 SAtk
Calm Nature
- Blizzard
- Giga Drain
- Leech Seed
- Substitute
Tentacruel (M) @ Black Sludge
Ability: Clear Body
EVs: 240 SDef / 252 HP / 16 Spd
Calm Nature
- Toxic Spikes
- Knock Off
- Rapid Spin
- Toxic
Avalugg (M) @ Leftovers
Ability: Ice Body
EVs: 252 Def / 252 HP / 4 Atk
Relaxed Nature
IVs: 0 Spd
- Avalanche
- Toxic
- Rapid Spin
- Gyro Ball
---- LEAD ----
Aerodactyl (M) @ Focus Sash
Ability: Unnerve
EVs: 252 Spd / 252 Atk / 4 HP
Jolly Nature
- Stealth Rock
- Taunt
- Rock Slide
- Earthquake
---- SWEEPERS ----
Azumarill (M) @ Leftovers
Ability: Huge Power
EVs: 252 Atk / 252 HP / 4 SDef
Adamant Nature
- Knock Off
- Waterfall
- Play Rough
- Aqua Jet
Dragonite (M) @ Leftovers
Ability: Multiscale
EVs: 252 Atk / 252 HP / 4 SDef
Adamant Nature
- Dragon Claw
- Extreme Speed
- Fire Punch
- Earthquake