Doan Mercenaries vs Maladian Assassins vs Massassi warriors vs. Vong
The Doan mercs that utterly humiliated Darth Bane vs the Maladian assassins that kicked Plagueis's ass vs the Massassi that hit Kun with a rock vs the Vong that took Darth Krayt captive
*Four warriors of each set
*Each team gets the standard gear they used when they encountered the Sith
*Each team gets an hour prep and knowledge of their opponent
Battle takes place in the Amazon forest
The mercenaries largely did as well as they did because of Cognus messing with Bane.
The Maladians are formidable and mentioned in the same breath as Mandalorian Death Watch, and quite dangerous at range with their decapitator disks, but there were three dozen of them in the attack, so it's no surprise they were almost victorious (despite reinforcements showing up).
Massassi are quite dangerous in melee, and naturally skilled warriors, but don't have the modern weaponry of the Maladians. While they do have some ranged weaponry, they specialize in close.
The Vong are basically Massassi in strength, but hard to sense in the force, well trained in both range and melee, and with better equipment.
I'd say Vong > Maladian > Massassi > Doan mercenary. Though Maladian vs Massassi is partially situational, Maladians better at range, Massassi in melee.
But only four actually fighting in this scenario. The number in the original situations just help us judge their strength.
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*Four warriors of each set
*Each team gets the standard gear they used when they encountered the Sith
*Each team gets an hour prep and knowledge of their opponent
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In this situation, *one* Vong may be able to kill the Mercs, the Maladians and Massassi are still dangerous, but not as much as the Vong.