Both Darmanitan and Krookodile are equally efficient, former having Sheer Force and learning Flare Blitz early, the latter having awesome abilities Intimidate and Moxie, learning Earthquake by level up and being capable of sweeping Caitlin and Shauntal, which Deino cannot achieve.
I would recommend Haxorus instead of Hydreigon, since the latter evolves so late (lvl 64, lvl 50 in case of Zweilous) and is available too late. Haxorus has the access of Dragon Dance and Mold Breaker which can sweep N and Ghetsis so easily. And Krookodile does handle Shauntal and Caitlin.
Ability: Mold Breaker (let's hope it to be mold breaker)
- Dragon Dance
- Dragon Claw
- X - Scissor
- Dig / Earthquake / any other move
Ability: Intimidate / Moxie (both are solid)
- Rock Slide
- Brick Break / Outrage / Strength
Bouffalant is alright, but you need to replace it with Darmanitan because Darmanitan hits harder, and is available very early.
Ability: Sheer Force
- Flare Blitz
- Rock Slide
Although, if I were to do that I'd have to spend extra time hunting for both and since Sandile has a greater chance to appear than Darmanitan I might Phase once or twice.
It might be difficult, but the result is worth it.
Hope this helps :)