I don't know if this was already discussed, but how about super troops for the added factions. I know this might sound that it might make them overpowered, but of course we can increase the rarity of these type soldiers. Here are my idea,
Elves: Corellon Chosen, these troops come from a prophecy of an ancient bloodline of elite elven warriors. Their swordsmanship and their magic is unmatched by most mortals. Also they're very fast and agile. They're rare in most cases though. Best way to deal with these guys is throw heavy armoured soldiers.
Orcs: Orc Beast, The very large variants of the orcs. They're almost as tall as an iron golem, and are very dangerous. Even though there are very slow, they have a monsterous damage rating and have a huge pool of health. Best way to deal with these guys is to stay far away from them or for a more strategic way, charming them to turn against their orc brothers.
Ridas: Grandmaster mages, their magic power is almost god like. They know ever spell there is and their magical power and defense is superior to most. Very rare in numbers, but 1 can be a huge problem to a huge company of men. They're also very skilled in using their staves as melee weapons. But their constitution is average of a veteran soldier. Best way to deal with these kind is throw heavy cavalry charges.
Drow: Beings of Loth, shadow like beings, their power, physical and magical, are very superior to many. They have great speed, great magical power and defense, great strength and great skill. Their one weakness is the lack of their kind. So they can easily get swarmed if left out of a crowd. Best way to fight this kind is of course, swarming them with Cavalry.
Dwarves: Mountain Keepers, very elite dwarves that are very skilled in melee and with a aquebus, they're nothing to take lightly at all, for their shooting ability is unmatched, and they can easily dominate a battle with axes. Best way to deal with these guys is throw non magical range power.
Blazing Hand: Angels like beings (couldn't come up with a specific name), these beings are descendants from another realm, fighting those who appose the balance of the world, or just provoke the blazing hand. Their magical ability is god like, as well as their melee ability with one handed weapons. They also have a good amount of speed. Best way to deal with these guys is swarms of heavily armoured troops or bows.
Undead Empire: Arch Liches, Past undead archmages that had once lived and ruled Ridas, but empowered by necromantic magic. They are very powerful in magic means, and necromancy. They can cause many troops to flee by their dark magic, and can easily destroy many troops with their deadly fire magic. Best way to deal with them is white magic.