Brave Bird Shiftry
Gives Shiftry a powerful option to catch Grass-types and Pinsir/Scyther on the switch, which will be really nice. The recoil's nasty, but since when did Swellow care? I do wonder if Shiftry has space for this, though.
Hydro Pump Gastro
Gives Gastrodon much more of an offensive presence, doing much more than a Scald + the fact that it can get boosts from Storm Drain. I personally prefer Scald, but this is still a nice addition.... AV Gastro, anyone?... I doubt that would become a thing, but, you know...
Dusknoir X Giratina
Flavor-wise, makes sense considering the fact that Dusknoir can drag people into the underworld, or as one would assume, the Distortion World. But anyway...
Gives it a strong STAB Ghost move to abuse. Would be nice if it wasn't a 2 turn move. Ghost doesn't have many switch-ins, but one Normal-type and you just wasted 1-2 turns. I would prefer Iron Fist to boost Shadow Punch or break the game and give it the CAP move Shadow Strike.
Ground/Dark Sandslash
STAB Knock Off to take out spinblockers is great and gives it another STAB move to use on offensive sets, like Sand Rush (Hippopotas is a thing, maybe?). Problem is that the new Fighting and Fairy weaknesses really hurt when Theorymon Mismagius and Gurdurr exist.
Bolt Strike Electivire and Searing Shot Magmortar
Gives these brothers highly spammable and very powerful STAB moves. Anything that doesn't resist Electric or Fire will have a hard time switching into Electivire and Magmortar respectively, and they have coverage to deal with the things that resist these moves. Extra note, Magmortar now has a spammable move that can spread status, which is lovely
Also, would Blue Flare Magmortar be too OP... You know, to complete the Zekrom and Reshiram thing?
My nomination: Iron Fist Dusclops + Dusknoir (+ Drain Punch maybe)
See the Dusknoir part of the post for short reasoning. If you've been in the Pet Mods part of the forums, you may recognize this as the same changes given to Dusknoir in the Movin' On Up thread, minus the stat changes.