Well, there's several Pokemon that can fit that criteria. Let's take a look at the weaknesses on resistances of each Pokemon:
Weaknesses:
Scizor: Fire
Rotom-W: Grass
Donphan: Ice, Grass, Water
Resistances:
Scizor: Bug, Steel, Poison, Dragon, Grass, Ice, Normal, Dark, Psychic, Ghost
Rotom-W: Flying, Water, Ice, Steel, Fire, Ground
Donphan: Rock, Electric, Poison*
Your Pokemon should have a Pokemon that is able to repeatedly take Fighting hits. For this reason, I suggest you add a Ghost Pokemon, such as Gengar or Chandelure, to the team. If you do that, a Special Wall is definitely recommended. Pokemon like Chansey, Blissey, Heatran (if not using Chandelure), or even a Latias can help in balancing out power and defenses. Consider adding a Physical attacker that will aid the team (Choiced if you Scizor isn't, and vice versa).
Funny thing is, I also made a team with this core, xD.
You can use my team as a guide. See it here.
