Vader as of A New Hope.
Malgus during his reign as the False Emperor.
Vader recruits Malgus so that they can overthrow the Emperor. Can they succeed? Palpatine is equipped with two of his lightsabers. Battle takes place on Hypori. Starting distance is 50 meters.
__________________ "Happiness is a lie. Life is horror. The light is always dying all across the universe. The last star will flicker out someday, when it does, all that remains is shadow. And I will be its king!"'-Amahl Farouk
__________________ "Vader's pulse and breathing were machine-regulated, so they could not quicken; but something in his chest became more electric around his meetings with the Emperor; he could not say how. A feeling of fullness, of power, of dark and demon mastery -- of secret lusts, unrestrained passion, wild submission -- all these things were in Vader's heart as he neared his Emperor. These things and more."
The 50 meters distance is a huge advantage to Sidious. He'd make the most of it going all-offensive with the Force. I'm not sure if they have enough defense to survive his attacks. If this was a close quarters fight, with say, 2 meters of separation, they'd put on a really good fight against him. I'd say they have a real good chance at defeating him.
__________________ "Happiness is a lie. Life is horror. The light is always dying all across the universe. The last star will flicker out someday, when it does, all that remains is shadow. And I will be its king!"'-Amahl Farouk
This won't be like Savage and Maul, or like Kit Fisto, Agen Kolar and company. These two are true powerhouses. Together at close range they could pose a significant threat to Sidious.
Not saying it'd be easy for anyone, though. If they do manage to defeat Sidious, it will certainly be an extremely long, painful duel in which both Sith would end up injured badly. I think it could go either way, saberwise. Vader has a speed disadvantage, other than the fact that Sidious knows him all too well.
The duo can do a combined two-person TK at a distance. They don't lack in ranged force either, and again, additive power.
Right. It'll be a pretty brutal fight, I picture. Vader and Malgus will take damage, but they're bricks, they *can* take damage, and output a lot of offense while doing so.