As many people have noted, the metagame is very fast-paced and one of the best ways to gain momentum is with a slow, bulky pivot. Rotom and Lando are extremely common as a result, but there's someone eelse lurking under the water (pun very much intended):
EelVestross
Eelektross @ Assault Vest
Quiet Nature
252 HP / 248 SpA / 8 SpD
- Volt Switch
- Knock Off
- Flamethrower
- Giga Drain / Acid Spray / Superpower
Sorry Sableye & Spiritomb, Eelektross is now the only Pokemon in the game with zero weaknesses. While it has solid stats all-around, it was held back previously by a lack of utility. XY has answered Eelektross' prayers! First of all, its giant offensive movepool is perfect for Assault Vest, packing a wonderfully slow STAB Volt Switch, the incredibly buffed Knock Off, and boatloads of coverage moves to choose from. Secondly, with 85/80/80 defenses, zero weaknesses (screw you Excadrill) and Assault Vest, he can easily tank most special threats and hit back hard.
Seems as a viable set, but why Giga Drain? Water-types won't be switching into you, and the only common Ground-type hit super effectively by it is Hippowdon, which you can't get past anyway, while it can just set up Stealth Rock and phaze you away. It's your best bet against Tyranitar, but you are doing jack shit to it and you are better off using Volt Switch as he comes in. I guess its nice for Mamoswine and Rotom-W, but that seems to be it. On the other hand, Drain Punch is a much more useful option. Drain Punch easily 2HKOes max HP Tyranitar, Excadrill (which avoids the 2HKO from Flamethrower with Assault Vest), is your best bet against Heatran (and can even 2HKO offensive variants if you use max Atk+), while in general providing way better coverage than Giga Drain and uses your superior Atk stat. Actually, it seems like a physically offensive set would work better, something like this:
Brave Nature:
252 HP / 252 Atk / 4 SpA
- U-turn
- Thunderbolt
- Drain Punch
- Knock Off
Those moves get perfect neutral coverage together, and a Fire move is not really needed when most Steel-types are covered by either Drain Punch (Ferrothorn, Heatran, Magnezone, Lucario, Excadrill), Thunderbolt (Skarmory, Forretress), or Knock Off (Aegislash). Same goes for Grass-types, most of which are covered by Knock Off (Celebi, Trevenant, Gourgeist, Roserade) or Drain Punch (Ferrothorn). U-turn > Volt Switch for guaranteed momentum, as otherwise you would need to predict correctly against Hippowdon (which would make you useless anyway, as you can't get past it), Excadrill, Garchomp, Landorus-T, etc. Of course you could use more SpA and fit HP Ice or Flamethrower somewhere there, as OHKOing Pokemon such as Landorus-T, Gliscor, Genesect, and Scizor can be huge, but it feels that most of the moves on the set are not easily replaced. U-turn means 100% free switches for your offensive Pokemon, Knock Off is amazing as everybody knows and covers quite a bit of threats, Thunderbolt is STAB, and Drain Punch is your best bet for recovery and getting past Excadrill, Tyranitar, and Heatran, which are everywhere.