Ambipom @ Normal Gem
252 Atk / 4 Def / 252 Spe
- Fake Out
- Power-Up Punch
- Double Hit
I've been running this set a lot lately and have found it very effective when used properly. I've only seen one out of 100+ Wifi Battles in XY so far so it is unexpected.
Unfortunately Low Seep got buffed from 60 BP to 65 BP so Ambipom no longer takes advantage of his Technician ability which is replaced with Power-Up Punch at 40 BP but the attack raise is nice. Usually Fake Out will nearly knock them out giving you a free Power-Up Punch.
Normal Gem is the only Gem currently available in XY and works well with Fake Out, unless it resists the hit this will do a lot of damage. Now Ambipom has no item and no way to hit Ghost types which is why Thief is there. And it's also handy as Thief got buffed from 40 BP to 60 BP in Gen VI.
Double Hit is his main STAB move and pretty standard adding up to an immense 105 BP. All moves take advantage of his Technician ability.
One thing to keep in mind is he's definitely not a sweeper by any means, he's very frail. But if you know when and how to use him it is a big threat. High risk high reward.