No no no no no. Like I said before on B3Ns RMT, Tyranitar in a Mono Dark Team is a stupid idea and an error if you add it in. Not only will you break Synergy, but you'll have an unnecessary Weather hurting your Team. Tyranitar gives Mono Dark Team no key resistances, a 4x weakness to Fighting, and nothing to toy with that a Scrafty cannot. So for specific details, follow my Answer on B3Ns RMT:
Here you go
Now, onto the replacements. The first thing I saw on this RMT that was completely wrong was the use of Murkrow over the Almighty Honchkrow. Why the hell would you make that mistake? Obviously, if you lack raw power in your Team, I'd suggest running Honchkrow, but Mandibuzz is also an awesome suggest if you decide to keep Tyranitar, as it gets Overcoat to not take Sand Damage. Suggested Movesets:
Honchkrow (M)@ Leftovers/Life Orb
EVs: 252 Atk / 4 SDef / 252 Sod
Adamant Nature(+Atk, -SAtk)
- Sucker Punch
- Brave Bird
Raw power in this Moveset. Take full abuse to it. The Set is self explanitory.
Mandibuzz (F)@ Leftovers
EVs: 248 HP / 8 Def / 252 SDef
Careful Nature (+SDef, -SAtk)
- Brave Bird
Basically a Special Wall. Moveset spreads Toxic around, while recovering with Roost and Scouting out or Attacking when Taunted. This Mandibuzz lures in a lot of Steel Types, so a Fighting Type Like Scrafty synergizes well with Mandibuzz.
Choice Specs > Wise Glasses. Choice Specs Hydreigon is a force to be reckoned with, and delivers way more damage than a lame Wise Glasses Variant.
Will-O-Wisp > Toxic. You got Mandibuzz to help spread Toxic Poison around, and Burning the Steel Types(except Heatran) will aid in Scrafty's sweep.
Night Shade > Mean Look. Honestly, Sableye wouldn't want to stay in on much Pokes in OU, and Night Shade will allow it to actually attack with a decent amount of damage. Way better option, unless you predict on Battling the greatest Type in the world, Psychic.
Life Orb > Muscle Band. You want Sharpedo to dish out as much damage as you can, and Life Orb is your best bet.
Protect > Aqua Jet. Protect is needed on Sharpedo, as it gives it a free Speed Boost to allow it to outspeed. Plus Gluguur is right, Aqua Jet is absolutely redundant on Sharpedo when it has Speed Boost equipped. Need to abuse this shark man.
I honestly hate this Guy, he absolutely sucks. Just like FrailCario in that regard, except Weavile is much much worse. It's Typing is absolutely horrible, dreadful. It's Movepool is nothing exciting except for a Swords Dance abuser(if it gets that?) Krookodile is obviously the superior option here, granting Synergy with Mandibuzz/ and all. Krookodile can also run a Choice Scarf Moveset, which you lack. So what's not to like in this guy?
Krookodile (M)@ Choice Scarf
EVs: 4 HP / 252 Atk / 252 Sod
Jolly Nature(+Spd, -SAtk)
- Stone Edge
Standard Scarf Krookodile.
These suggestions can fit in with Tyranitar, but I wouldn't run Tyranitar here. If you really want to run it, then a Water resister in Cacturne is necessary to tank them for Krookodile and Tyranitar. For Tyranitar replacements, Bisharp and Scrafty come to mind as best, due to how they fit well in the Team, providing Stealth Rock from the former and Sweeping with ease from the latter. Those two ate the only Pokes I'd recommend. Comment if you want a Moveset for either one of them.