Here is a nice little combo i have been using lately:
Trevenant @ Sitrus Berry
Ability: Harvest
EVs: 252 HP / 140 SpD / 116 Spe
Careful Nature
- Will-O-Wisp
- Leech Seed
- Substitute
- Phantom Force
+
Blaziken @ Leftovers
Ability: Speed Boost
EVs: 4 HP / 252 SpA / 252 Spe
Timid Nature
- Substitute
- Protect
- Baton Pass
- Fire Blast
The strategy is simple: set up a Substitute with Blaziken on something you scare out, as Gyarados / Azumarill / Slowbro / Rotom-W switch into you. Then either Baton Pass immediately the Sub with a +1 Speed boost, or if you know that the opponent can't set up use Protect to grab a second Speed boost and Baton Pass the next turn. Trevenant can easily switch into Water attacks from those Pokemon and start stalling the shit out of everything. Even if Azumarill went for Play Rough you can still bring Trevenant in for free thanks to Sub, burn Azumarill with WoW, and then slowly stall it out. Honestly, this Trevenant is outright crazy with a few Speed boosts. At +2 it outspeeds everything up to base 110s, such as Gengar, can burn physical attackers before they can move and slowly stall them out or throw a Leech Seed to special attackers, take most special hits from full life with its good special bulk, and start stall them to death too. If you do this right and you have taken Fire-types out, Trevenant can easily clean whole teams by itself. Obviously hazard support makes this strategy even more effective.
Trevenant's EV spread is this of the second set on its preview, with enough Speed to outrun min Speed Skarmory, Scizor, and Tyranitar (so you can burn them before they can fuck you up with Brave Bird / Pursuit / U-turn / Crunch) and the rest to special bulk as its typing is more suited to tanking special attacks. Blaziken's spread allows it to 2HKO physically defensive Hippowdon, a common answer to SubPass Blaziken, as well as OHKO most Steel-types and dent Aegislash while avoiding King's Shield. It is also fast enough to outrun Modest Choice Scarf Rotom-W after one Protect, so it can set up on its face and Baton Pass to Trevenant.
Just make sure to carry something to deal with Fire-types, especially Talonflame, which can fuck up both Pokemon with priority Brave Bird, and you are good to go.