I love balanced Hackmons. Here's a few things from my factory of weirdness.
This is a lead I've been toying with. It needs a bit of help.
Deoxys-S @ Lum Berry
Timid (+Spe, -Atk)
So the idea here is information/disruption. Basically, find out what my opponent has, then either Sleep them with a faster Spore (Prankster), set up hazards, Taunt, or Baton Pass out to see if I can get a good matchup if they switch out. I might swap out Taunt for Substitute though given the insane amount of Magic Coat users.
Registeel @ Leftovers
Careful (+SpD, -SpA)
Ability: Flash Fire
I initially made this as a counter to Contrary Reshiram. Registeel has fantastic bulk, and Steel + Flash Fire gives it a resistance to Dragon + Fire. Not only that, it resists Stored Power and Extremespeed, so it can usually get the drop on opposing mons using those strategies. Flash Fire also prevents it from burns since basically nothing uses Scald in hackmons, and once activated it basically has Fire STAB. Hackmons is so volatile that one action your opponent gives up can cost them a game (e.g. if Slaking gets greedy after Belly Drum and tries Sacred Fire, Registeel absorbs it, Heart Swaps the attack boost, and proceeds to crush all enemies.
Dialga @ Leftovers
Bold (+Def, -Atk)
Ability: Mold Breaker
Pretty straightforward. Basically I looked at Dialga as a very good balance of resistances and stats, and decided it'd be a pretty epic QD Sweeper (100 HP, 120 Def, 150 SpA). Mold Breaker lets it Toxic bulky Magic Bounce mons, Dragon Pulse straight through Sturdy Shedinja. It might not be the best mon for this role, but it does at least resist ESpeed and nobody seems to use Fighting priority.
Otherwise I've made a sand team. Sandstream screws Shedinja and cuts the bulkiness of a lot of mons. I used Regirock as the SS Starter since it has the highest bulk in Sand without using an item (hi Eviolite Rhydon)